tools/nolibc: make compiler and assembler agree on the section around _start
The out-of-block asm() statement carrying _start does not allow the compiler to know what section the assembly code is being emitted to, and there's no easy way to push/pop the current section and restore it. It sometimes causes issues depending on the include files ordering and compiler optimizations. For example if a variable is declared immediately before the asm() block and another one after, the compiler assumes that the current section is still .bss and doesn't re-emit it, making the second variable appear inside the .text section instead. Forcing .bss at the end of the _start block doesn't work either because at certain optimizations the compiler may reorder blocks and will make some real code appear just after this block. A significant number of solutions were attempted, but many of them were still sensitive to section reordering. In the end, the best way to make sure the compiler and assembler agree on the current section is to place this code inside a function. Here the function is directly called _start and configured not to emit a frame-pointer, hence to have no prologue. If some future architectures would still emit some prologue, another working approach consists in naming the function differently and placing the _start label inside the asm statement. But the current solution is simpler. It was tested with nolibc-test at -O,-O0,-O2,-O3,-Os for arm,arm64,i386, mips,riscv,s390 and x86_64. Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Willy Tarreau
Paul E. McKenney
parent
28ef4c3753
commit
7f85485896
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@ -182,18 +182,19 @@ struct sys_stat_struct {
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})
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/* startup code */
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__asm__ (".section .text\n"
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".weak _start\n"
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"_start:\n"
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"ldr x0, [sp]\n" // argc (x0) was in the stack
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"add x1, sp, 8\n" // argv (x1) = sp
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"lsl x2, x0, 3\n" // envp (x2) = 8*argc ...
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"add x2, x2, 8\n" // + 8 (skip null)
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"add x2, x2, x1\n" // + argv
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"and sp, x1, -16\n" // sp must be 16-byte aligned in the callee
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"bl main\n" // main() returns the status code, we'll exit with it.
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"mov x8, 93\n" // NR_exit == 93
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"svc #0\n"
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"");
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
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{
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__asm__ volatile (
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"ldr x0, [sp]\n" // argc (x0) was in the stack
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"add x1, sp, 8\n" // argv (x1) = sp
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"lsl x2, x0, 3\n" // envp (x2) = 8*argc ...
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"add x2, x2, 8\n" // + 8 (skip null)
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"add x2, x2, x1\n" // + argv
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"and sp, x1, -16\n" // sp must be 16-byte aligned in the callee
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"bl main\n" // main() returns the status code, we'll exit with it.
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"mov x8, 93\n" // NR_exit == 93
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"svc #0\n"
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);
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__builtin_unreachable();
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}
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#endif // _NOLIBC_ARCH_AARCH64_H
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@ -175,30 +175,20 @@ struct sys_stat_struct {
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})
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/* startup code */
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__asm__ (".section .text\n"
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".weak _start\n"
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"_start:\n"
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#if defined(__THUMBEB__) || defined(__THUMBEL__)
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/* We enter here in 32-bit mode but if some previous functions were in
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* 16-bit mode, the assembler cannot know, so we need to tell it we're in
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* 32-bit now, then switch to 16-bit (is there a better way to do it than
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* adding 1 by hand ?) and tell the asm we're now in 16-bit mode so that
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* it generates correct instructions. Note that we do not support thumb1.
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*/
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".code 32\n"
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"add r0, pc, #1\n"
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"bx r0\n"
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".code 16\n"
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#endif
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"pop {%r0}\n" // argc was in the stack
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"mov %r1, %sp\n" // argv = sp
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"add %r2, %r1, %r0, lsl #2\n" // envp = argv + 4*argc ...
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"add %r2, %r2, $4\n" // ... + 4
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"and %r3, %r1, $-8\n" // AAPCS : sp must be 8-byte aligned in the
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"mov %sp, %r3\n" // callee, an bl doesn't push (lr=pc)
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"bl main\n" // main() returns the status code, we'll exit with it.
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"movs r7, $1\n" // NR_exit == 1
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"svc $0x00\n"
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"");
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
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{
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__asm__ volatile (
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"pop {%r0}\n" // argc was in the stack
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"mov %r1, %sp\n" // argv = sp
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"add %r2, %r1, %r0, lsl #2\n" // envp = argv + 4*argc ...
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"add %r2, %r2, $4\n" // ... + 4
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"and %r3, %r1, $-8\n" // AAPCS : sp must be 8-byte aligned in the
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"mov %sp, %r3\n" // callee, an bl doesn't push (lr=pc)
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"bl main\n" // main() returns the status code, we'll exit with it.
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"movs r7, $1\n" // NR_exit == 1
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"svc $0x00\n"
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);
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__builtin_unreachable();
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}
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#endif // _NOLIBC_ARCH_ARM_H
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@ -197,23 +197,25 @@ struct sys_stat_struct {
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* 2) The deepest stack frame should be set to zero
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*
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*/
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__asm__ (".section .text\n"
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".weak _start\n"
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"_start:\n"
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"pop %eax\n" // argc (first arg, %eax)
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"mov %esp, %ebx\n" // argv[] (second arg, %ebx)
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"lea 4(%ebx,%eax,4),%ecx\n" // then a NULL then envp (third arg, %ecx)
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"xor %ebp, %ebp\n" // zero the stack frame
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"and $-16, %esp\n" // x86 ABI : esp must be 16-byte aligned before
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"sub $4, %esp\n" // the call instruction (args are aligned)
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"push %ecx\n" // push all registers on the stack so that we
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"push %ebx\n" // support both regparm and plain stack modes
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"push %eax\n"
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"call main\n" // main() returns the status code in %eax
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"mov %eax, %ebx\n" // retrieve exit code (32-bit int)
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"movl $1, %eax\n" // NR_exit == 1
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"int $0x80\n" // exit now
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"hlt\n" // ensure it does not
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"");
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
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{
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__asm__ volatile (
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"pop %eax\n" // argc (first arg, %eax)
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"mov %esp, %ebx\n" // argv[] (second arg, %ebx)
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"lea 4(%ebx,%eax,4),%ecx\n" // then a NULL then envp (third arg, %ecx)
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"xor %ebp, %ebp\n" // zero the stack frame
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"and $-16, %esp\n" // x86 ABI : esp must be 16-byte aligned before
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"sub $4, %esp\n" // the call instruction (args are aligned)
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"push %ecx\n" // push all registers on the stack so that we
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"push %ebx\n" // support both regparm and plain stack modes
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"push %eax\n"
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"call main\n" // main() returns the status code in %eax
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"mov %eax, %ebx\n" // retrieve exit code (32-bit int)
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"movl $1, %eax\n" // NR_exit == 1
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"int $0x80\n" // exit now
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"hlt\n" // ensure it does not
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);
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__builtin_unreachable();
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}
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#endif // _NOLIBC_ARCH_I386_H
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@ -189,29 +189,32 @@ struct sys_stat_struct {
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})
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/* startup code, note that it's called __start on MIPS */
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__asm__ (".section .text\n"
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".weak __start\n"
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".set nomips16\n"
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".set push\n"
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".set noreorder\n"
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".option pic0\n"
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".ent __start\n"
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"__start:\n"
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"lw $a0,($sp)\n" // argc was in the stack
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"addiu $a1, $sp, 4\n" // argv = sp + 4
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"sll $a2, $a0, 2\n" // a2 = argc * 4
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"add $a2, $a2, $a1\n" // envp = argv + 4*argc ...
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"addiu $a2, $a2, 4\n" // ... + 4
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"li $t0, -8\n"
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"and $sp, $sp, $t0\n" // sp must be 8-byte aligned
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"addiu $sp,$sp,-16\n" // the callee expects to save a0..a3 there!
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"jal main\n" // main() returns the status code, we'll exit with it.
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"nop\n" // delayed slot
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"move $a0, $v0\n" // retrieve 32-bit exit code from v0
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"li $v0, 4001\n" // NR_exit == 4001
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"syscall\n"
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".end __start\n"
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".set pop\n"
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"");
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __start(void)
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{
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__asm__ volatile (
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//".set nomips16\n"
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".set push\n"
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".set noreorder\n"
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".option pic0\n"
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//".ent __start\n"
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//"__start:\n"
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"lw $a0,($sp)\n" // argc was in the stack
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"addiu $a1, $sp, 4\n" // argv = sp + 4
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"sll $a2, $a0, 2\n" // a2 = argc * 4
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"add $a2, $a2, $a1\n" // envp = argv + 4*argc ...
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"addiu $a2, $a2, 4\n" // ... + 4
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"li $t0, -8\n"
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"and $sp, $sp, $t0\n" // sp must be 8-byte aligned
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"addiu $sp,$sp,-16\n" // the callee expects to save a0..a3 there!
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"jal main\n" // main() returns the status code, we'll exit with it.
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"nop\n" // delayed slot
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"move $a0, $v0\n" // retrieve 32-bit exit code from v0
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"li $v0, 4001\n" // NR_exit == 4001
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"syscall\n"
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//".end __start\n"
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".set pop\n"
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);
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__builtin_unreachable();
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}
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#endif // _NOLIBC_ARCH_MIPS_H
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@ -183,22 +183,24 @@ struct sys_stat_struct {
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})
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/* startup code */
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__asm__ (".section .text\n"
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".weak _start\n"
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"_start:\n"
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".option push\n"
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".option norelax\n"
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"lla gp, __global_pointer$\n"
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".option pop\n"
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"lw a0, 0(sp)\n" // argc (a0) was in the stack
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"add a1, sp, "SZREG"\n" // argv (a1) = sp
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"slli a2, a0, "PTRLOG"\n" // envp (a2) = SZREG*argc ...
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"add a2, a2, "SZREG"\n" // + SZREG (skip null)
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"add a2,a2,a1\n" // + argv
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"andi sp,a1,-16\n" // sp must be 16-byte aligned
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"call main\n" // main() returns the status code, we'll exit with it.
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"li a7, 93\n" // NR_exit == 93
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"ecall\n"
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"");
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
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{
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__asm__ volatile (
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".option push\n"
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".option norelax\n"
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"lla gp, __global_pointer$\n"
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".option pop\n"
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"lw a0, 0(sp)\n" // argc (a0) was in the stack
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"add a1, sp, "SZREG"\n" // argv (a1) = sp
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"slli a2, a0, "PTRLOG"\n" // envp (a2) = SZREG*argc ...
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"add a2, a2, "SZREG"\n" // + SZREG (skip null)
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"add a2,a2,a1\n" // + argv
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"andi sp,a1,-16\n" // sp must be 16-byte aligned
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"call main\n" // main() returns the status code, we'll exit with it.
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"li a7, 93\n" // NR_exit == 93
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"ecall\n"
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);
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__builtin_unreachable();
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}
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#endif // _NOLIBC_ARCH_RISCV_H
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@ -172,27 +172,29 @@ struct sys_stat_struct {
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})
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/* startup code */
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__asm__ (".section .text\n"
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".weak _start\n"
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"_start:\n"
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"lg %r2,0(%r15)\n" /* argument count */
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"la %r3,8(%r15)\n" /* argument pointers */
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
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{
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__asm__ volatile (
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"lg %r2,0(%r15)\n" /* argument count */
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"la %r3,8(%r15)\n" /* argument pointers */
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"xgr %r0,%r0\n" /* r0 will be our NULL value */
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/* search for envp */
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"lgr %r4,%r3\n" /* start at argv */
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"0:\n"
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"clg %r0,0(%r4)\n" /* entry zero? */
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"la %r4,8(%r4)\n" /* advance pointer */
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"jnz 0b\n" /* no -> test next pointer */
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/* yes -> r4 now contains start of envp */
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"xgr %r0,%r0\n" /* r0 will be our NULL value */
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/* search for envp */
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"lgr %r4,%r3\n" /* start at argv */
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"0:\n"
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"clg %r0,0(%r4)\n" /* entry zero? */
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"la %r4,8(%r4)\n" /* advance pointer */
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"jnz 0b\n" /* no -> test next pointer */
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/* yes -> r4 now contains start of envp */
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"aghi %r15,-160\n" /* allocate new stackframe */
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"xc 0(8,%r15),0(%r15)\n" /* clear backchain */
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"brasl %r14,main\n" /* ret value of main is arg to exit */
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"lghi %r1,1\n" /* __NR_exit */
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"svc 0\n"
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"");
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"aghi %r15,-160\n" /* allocate new stackframe */
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"xc 0(8,%r15),0(%r15)\n" /* clear backchain */
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"brasl %r14,main\n" /* ret value of main is arg to exit */
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"lghi %r1,1\n" /* __NR_exit */
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"svc 0\n"
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);
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__builtin_unreachable();
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}
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struct s390_mmap_arg_struct {
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unsigned long addr;
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@ -197,19 +197,21 @@ struct sys_stat_struct {
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* 2) The deepest stack frame should be zero (the %rbp).
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*
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*/
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__asm__ (".section .text\n"
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".weak _start\n"
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"_start:\n"
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"pop %rdi\n" // argc (first arg, %rdi)
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"mov %rsp, %rsi\n" // argv[] (second arg, %rsi)
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"lea 8(%rsi,%rdi,8),%rdx\n" // then a NULL then envp (third arg, %rdx)
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"xor %ebp, %ebp\n" // zero the stack frame
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"and $-16, %rsp\n" // x86 ABI : esp must be 16-byte aligned before call
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"call main\n" // main() returns the status code, we'll exit with it.
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"mov %eax, %edi\n" // retrieve exit code (32 bit)
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"mov $60, %eax\n" // NR_exit == 60
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"syscall\n" // really exit
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"hlt\n" // ensure it does not return
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"");
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void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
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{
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__asm__ volatile (
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"pop %rdi\n" // argc (first arg, %rdi)
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"mov %rsp, %rsi\n" // argv[] (second arg, %rsi)
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"lea 8(%rsi,%rdi,8),%rdx\n" // then a NULL then envp (third arg, %rdx)
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"xor %ebp, %ebp\n" // zero the stack frame
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"and $-16, %rsp\n" // x86 ABI : esp must be 16-byte aligned before call
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"call main\n" // main() returns the status code, we'll exit with it.
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"mov %eax, %edi\n" // retrieve exit code (32 bit)
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"mov $60, %eax\n" // NR_exit == 60
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"syscall\n" // really exit
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"hlt\n" // ensure it does not return
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);
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__builtin_unreachable();
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}
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#endif // _NOLIBC_ARCH_X86_64_H
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