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[ELF] --wrap: Drop __real_ symbol from the symbol table 

In D34993, we discussed and concluded that we should drop `__real_
symbol from the symbol table, but I did the opposite in D50569.
This patch is to drop `__real_` symbol.

MaskRay's note: omitting `__real_` is important if it is undefined:
otherwise a subsequent link may error due to the undefined `__real_` in .dynsym

Differential Revision: https://reviews.llvm.org/D51283
This commit is contained in:
Rui Ueyama 2020-05-27 16:18:55 -07:00 committed by Fangrui Song
parent 2bf3fe9b6d
commit 54d2896852
4 changed files with 28 additions and 32 deletions
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14
lld/ELF/SymbolTable.cpp
View File

@ -40,12 +40,14 @@ void SymbolTable::wrap(Symbol *sym, Symbol *real, Symbol *wrap) {
idx2 = idx1;
idx1 = idx3;
// Now renaming is complete. No one refers Real symbol. We could leave
// Real as-is, but if Real is written to the symbol table, that may
// contain irrelevant values. So, we copy all values from Sym to Real.
StringRef s = real->getName();
memcpy(real, sym, sizeof(SymbolUnion));
real->setName(s);
// Now renaming is complete, and no one refers to real. We drop real from
// .symtab and .dynsym. If real is undefined, it is important that we don't
// leave it in .dynsym, because otherwise it might lead to an undefined symbol
// error in a subsequent link. If real is defined, we could emit real as an
// alias for sym, but that could degrade the user experience of some tools
// that can print out only one symbol for each location: sym is a preferred
// name than real, but they might print out real instead.
real->isUsedInRegularObj = false;
}
// Find an existing symbol or create a new one.

4
lld/test/ELF/lto/wrap-2.ll
View File

@ -27,10 +27,6 @@
; BIND-NEXT: Value:
; BIND-NEXT: Size:
; BIND-NEXT: Binding: Local
; BIND: Name: __real_bar
; BIND-NEXT: Value:
; BIND-NEXT: Size:
; BIND-NEXT: Binding: Local
; BIND: Name: __wrap_bar
; BIND-NEXT: Value:
; BIND-NEXT: Size:

35
lld/test/ELF/wrap-no-real.s
View File

@ -5,27 +5,30 @@
// RUN: ld.lld -o %t3.so -shared %t3.o
// RUN: ld.lld -o %t %t1.o %t2.o -wrap foo
// RUN: llvm-objdump -d --print-imm-hex %t | FileCheck %s
// RUN: ld.lld -o %t %t1.o %t2.o %t3.so -wrap foo
// RUN: llvm-objdump -d --print-imm-hex %t | FileCheck %s
// RUN: llvm-objdump -d %t | FileCheck %s
// RUN: llvm-readelf -s -x .got %t | FileCheck --check-prefix=READELF --implicit-check-not=__real_ %s
// CHECK: <_start>:
// CHECK-NEXT: movl $0x11010, %edx
// CHECK-NEXT: movl $0x11010, %edx
// CHECK-NEXT: movl $0x11000, %edx
// CHECK-NEXT: movq {{.*}}(%rip), %rax # 2021a8
// CHECK-NEXT: movq {{.*}}(%rip), %rbx # 2021a8
// CHECK-NEXT: movq {{.*}}(%rip), %rcx # 2021b0
// RUN: llvm-objdump -t %t | FileCheck --check-prefix=SYM %s
// READELF: 0000000000011010 0 NOTYPE GLOBAL DEFAULT ABS __wrap_foo
// READELF: 0000000000011000 0 NOTYPE GLOBAL DEFAULT ABS foo
// READELF: Hex dump of section '.got':
// READELF-NEXT: 0x[[#%x,ADDR:]] 10100100 00000000 00100100 00000000
// RUN: ld.lld -o %t2 %t1.o %t2.o %t3.so --wrap foo
// RUN: llvm-objdump -d %t2 | FileCheck --check-prefix=CHECK2 %s
// RUN: llvm-readelf -s -x .got %t2 | FileCheck --check-prefix=READELF --implicit-check-not=__real_ %s
// SYM: {{.*}} l .dynamic 0000000000000000 .hidden _DYNAMIC
// SYM-NEXT: 0000000000011000 g *ABS* 0000000000000000 __real_foo
// SYM-NEXT: 0000000000011010 g *ABS* 0000000000000000 __wrap_foo
// SYM-NEXT: {{.*}} g .text 0000000000000000 _start
// SYM-NEXT: 0000000000011000 g *ABS* 0000000000000000 foo
// CHECK2: <_start>:
// CHECK2-NEXT: movq {{.*}}(%rip), %rax # 2022f8
// CHECK2-NEXT: movq {{.*}}(%rip), %rbx # 2022f8
// CHECK2-NEXT: movq {{.*}}(%rip), %rcx # 202300
.global _start
_start:
movl $foo, %edx
movl $__wrap_foo, %edx
movl $__real_foo, %edx
mov foo@gotpcrel(%rip), %rax
mov __wrap_foo@gotpcrel(%rip), %rbx
mov __real_foo@gotpcrel(%rip), %rcx

7
lld/test/ELF/wrap.s
View File

@ -33,12 +33,7 @@
// SYM2-NEXT: Other [
// SYM2-NEXT: STV_PROTECTED
// SYM2-NEXT: ]
// SYM3: Name: __real_foo
// SYM3-NEXT: Value: 0x11000
// SYM3-NEXT: Size:
// SYM3-NEXT: Binding: Global
// SYM3-NEXT: Type: None
// SYM3-NEXT: Other: 0
// SYM3-NOT: Name: __real_foo
.global _start
_start: