forked from OSchip/llvm-project
5 Commits
Author | SHA1 | Message | Date |
---|---|---|---|
Yonghong Song | 05e46979d2 |
[BPF] do compile-once run-everywhere relocation for bitfields
A bpf specific clang intrinsic is introduced: u32 __builtin_preserve_field_info(member_access, info_kind) Depending on info_kind, different information will be returned to the program. A relocation is also recorded for this builtin so that bpf loader can patch the instruction on the target host. This clang intrinsic is used to get certain information to facilitate struct/union member relocations. The offset relocation is extended by 4 bytes to include relocation kind. Currently supported relocation kinds are enum { FIELD_BYTE_OFFSET = 0, FIELD_BYTE_SIZE, FIELD_EXISTENCE, FIELD_SIGNEDNESS, FIELD_LSHIFT_U64, FIELD_RSHIFT_U64, }; for __builtin_preserve_field_info. The old access offset relocation is covered by FIELD_BYTE_OFFSET = 0. An example: struct s { int a; int b1:9; int b2:4; }; enum { FIELD_BYTE_OFFSET = 0, FIELD_BYTE_SIZE, FIELD_EXISTENCE, FIELD_SIGNEDNESS, FIELD_LSHIFT_U64, FIELD_RSHIFT_U64, }; void bpf_probe_read(void *, unsigned, const void *); int field_read(struct s *arg) { unsigned long long ull = 0; unsigned offset = __builtin_preserve_field_info(arg->b2, FIELD_BYTE_OFFSET); unsigned size = __builtin_preserve_field_info(arg->b2, FIELD_BYTE_SIZE); #ifdef USE_PROBE_READ bpf_probe_read(&ull, size, (const void *)arg + offset); unsigned lshift = __builtin_preserve_field_info(arg->b2, FIELD_LSHIFT_U64); #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ lshift = lshift + (size << 3) - 64; #endif #else switch(size) { case 1: ull = *(unsigned char *)((void *)arg + offset); break; case 2: ull = *(unsigned short *)((void *)arg + offset); break; case 4: ull = *(unsigned int *)((void *)arg + offset); break; case 8: ull = *(unsigned long long *)((void *)arg + offset); break; } unsigned lshift = __builtin_preserve_field_info(arg->b2, FIELD_LSHIFT_U64); #endif ull <<= lshift; if (__builtin_preserve_field_info(arg->b2, FIELD_SIGNEDNESS)) return (long long)ull >> __builtin_preserve_field_info(arg->b2, FIELD_RSHIFT_U64); return ull >> __builtin_preserve_field_info(arg->b2, FIELD_RSHIFT_U64); } There is a minor overhead for bpf_probe_read() on big endian. The code and relocation generated for field_read where bpf_probe_read() is used to access argument data on little endian mode: r3 = r1 r1 = 0 r1 = 4 <=== relocation (FIELD_BYTE_OFFSET) r3 += r1 r1 = r10 r1 += -8 r2 = 4 <=== relocation (FIELD_BYTE_SIZE) call bpf_probe_read r2 = 51 <=== relocation (FIELD_LSHIFT_U64) r1 = *(u64 *)(r10 - 8) r1 <<= r2 r2 = 60 <=== relocation (FIELD_RSHIFT_U64) r0 = r1 r0 >>= r2 r3 = 1 <=== relocation (FIELD_SIGNEDNESS) if r3 == 0 goto LBB0_2 r1 s>>= r2 r0 = r1 LBB0_2: exit Compare to the above code between relocations FIELD_LSHIFT_U64 and FIELD_LSHIFT_U64, the code with big endian mode has four more instructions. r1 = 41 <=== relocation (FIELD_LSHIFT_U64) r6 += r1 r6 += -64 r6 <<= 32 r6 >>= 32 r1 = *(u64 *)(r10 - 8) r1 <<= r6 r2 = 60 <=== relocation (FIELD_RSHIFT_U64) The code and relocation generated when using direct load. r2 = 0 r3 = 4 r4 = 4 if r4 s> 3 goto LBB0_3 if r4 == 1 goto LBB0_5 if r4 == 2 goto LBB0_6 goto LBB0_9 LBB0_6: # %sw.bb1 r1 += r3 r2 = *(u16 *)(r1 + 0) goto LBB0_9 LBB0_3: # %entry if r4 == 4 goto LBB0_7 if r4 == 8 goto LBB0_8 goto LBB0_9 LBB0_8: # %sw.bb9 r1 += r3 r2 = *(u64 *)(r1 + 0) goto LBB0_9 LBB0_5: # %sw.bb r1 += r3 r2 = *(u8 *)(r1 + 0) goto LBB0_9 LBB0_7: # %sw.bb5 r1 += r3 r2 = *(u32 *)(r1 + 0) LBB0_9: # %sw.epilog r1 = 51 r2 <<= r1 r1 = 60 r0 = r2 r0 >>= r1 r3 = 1 if r3 == 0 goto LBB0_11 r2 s>>= r1 r0 = r2 LBB0_11: # %sw.epilog exit Considering verifier is able to do limited constant propogation following branches. The following is the code actually traversed. r2 = 0 r3 = 4 <=== relocation r4 = 4 <=== relocation if r4 s> 3 goto LBB0_3 LBB0_3: # %entry if r4 == 4 goto LBB0_7 LBB0_7: # %sw.bb5 r1 += r3 r2 = *(u32 *)(r1 + 0) LBB0_9: # %sw.epilog r1 = 51 <=== relocation r2 <<= r1 r1 = 60 <=== relocation r0 = r2 r0 >>= r1 r3 = 1 if r3 == 0 goto LBB0_11 r2 s>>= r1 r0 = r2 LBB0_11: # %sw.epilog exit For native load case, the load size is calculated to be the same as the size of load width LLVM otherwise used to load the value which is then used to extract the bitfield value. Differential Revision: https://reviews.llvm.org/D67980 llvm-svn: 374099 |
|
Yonghong Song | d3d88d08b5 |
[BPF] Support for compile once and run everywhere
Introduction ============ This patch added intial support for bpf program compile once and run everywhere (CO-RE). The main motivation is for bpf program which depends on kernel headers which may vary between different kernel versions. The initial discussion can be found at https://lwn.net/Articles/773198/. Currently, bpf program accesses kernel internal data structure through bpf_probe_read() helper. The idea is to capture the kernel data structure to be accessed through bpf_probe_read() and relocate them on different kernel versions. On each host, right before bpf program load, the bpfloader will look at the types of the native linux through vmlinux BTF, calculates proper access offset and patch the instruction. To accommodate this, three intrinsic functions preserve_{array,union,struct}_access_index are introduced which in clang will preserve the base pointer, struct/union/array access_index and struct/union debuginfo type information. Later, bpf IR pass can reconstruct the whole gep access chains without looking at gep itself. This patch did the following: . An IR pass is added to convert preserve_*_access_index to global variable who name encodes the getelementptr access pattern. The global variable has metadata attached to describe the corresponding struct/union debuginfo type. . An SimplifyPatchable MachineInstruction pass is added to remove unnecessary loads. . The BTF output pass is enhanced to generate relocation records located in .BTF.ext section. Typical CO-RE also needs support of global variables which can be assigned to different values to different hosts. For example, kernel version can be used to guard different versions of codes. This patch added the support for patchable externals as well. Example ======= The following is an example. struct pt_regs { long arg1; long arg2; }; struct sk_buff { int i; struct net_device *dev; }; #define _(x) (__builtin_preserve_access_index(x)) static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr) = (void *) 4; extern __attribute__((section(".BPF.patchable_externs"))) unsigned __kernel_version; int bpf_prog(struct pt_regs *ctx) { struct net_device *dev = 0; // ctx->arg* does not need bpf_probe_read if (__kernel_version >= 41608) bpf_probe_read(&dev, sizeof(dev), _(&((struct sk_buff *)ctx->arg1)->dev)); else bpf_probe_read(&dev, sizeof(dev), _(&((struct sk_buff *)ctx->arg2)->dev)); return dev != 0; } In the above, we want to translate the third argument of bpf_probe_read() as relocations. -bash-4.4$ clang -target bpf -O2 -g -S trace.c The compiler will generate two new subsections in .BTF.ext, OffsetReloc and ExternReloc. OffsetReloc is to record the structure member offset operations, and ExternalReloc is to record the external globals where only u8, u16, u32 and u64 are supported. BPFOffsetReloc Size struct SecLOffsetReloc for ELF section #1 A number of struct BPFOffsetReloc for ELF section #1 struct SecOffsetReloc for ELF section #2 A number of struct BPFOffsetReloc for ELF section #2 ... BPFExternReloc Size struct SecExternReloc for ELF section #1 A number of struct BPFExternReloc for ELF section #1 struct SecExternReloc for ELF section #2 A number of struct BPFExternReloc for ELF section #2 struct BPFOffsetReloc { uint32_t InsnOffset; ///< Byte offset in this section uint32_t TypeID; ///< TypeID for the relocation uint32_t OffsetNameOff; ///< The string to traverse types }; struct BPFExternReloc { uint32_t InsnOffset; ///< Byte offset in this section uint32_t ExternNameOff; ///< The string for external variable }; Note that only externs with attribute section ".BPF.patchable_externs" are considered for Extern Reloc which will be patched by bpf loader right before the load. For the above test case, two offset records and one extern record will be generated: OffsetReloc records: .long .Ltmp12 # Insn Offset .long 7 # TypeId .long 242 # Type Decode String .long .Ltmp18 # Insn Offset .long 7 # TypeId .long 242 # Type Decode String ExternReloc record: .long .Ltmp5 # Insn Offset .long 165 # External Variable In string table: .ascii "0:1" # string offset=242 .ascii "__kernel_version" # string offset=165 The default member offset can be calculated as the 2nd member offset (0 representing the 1st member) of struct "sk_buff". The asm code: .Ltmp5: .Ltmp6: r2 = 0 r3 = 41608 .Ltmp7: .Ltmp8: .loc 1 18 9 is_stmt 0 # t.c:18:9 .Ltmp9: if r3 > r2 goto LBB0_2 .Ltmp10: .Ltmp11: .loc 1 0 9 # t.c:0:9 .Ltmp12: r2 = 8 .Ltmp13: .loc 1 19 66 is_stmt 1 # t.c:19:66 .Ltmp14: .Ltmp15: r3 = *(u64 *)(r1 + 0) goto LBB0_3 .Ltmp16: .Ltmp17: LBB0_2: .loc 1 0 66 is_stmt 0 # t.c:0:66 .Ltmp18: r2 = 8 .loc 1 21 66 is_stmt 1 # t.c:21:66 .Ltmp19: r3 = *(u64 *)(r1 + 8) .Ltmp20: .Ltmp21: LBB0_3: .loc 1 0 66 is_stmt 0 # t.c:0:66 r3 += r2 r1 = r10 .Ltmp22: .Ltmp23: .Ltmp24: r1 += -8 r2 = 8 call 4 For instruction .Ltmp12 and .Ltmp18, "r2 = 8", the number 8 is the structure offset based on the current BTF. Loader needs to adjust it if it changes on the host. For instruction .Ltmp5, "r2 = 0", the external variable got a default value 0, loader needs to supply an appropriate value for the particular host. Compiling to generate object code and disassemble: 0000000000000000 bpf_prog: 0: b7 02 00 00 00 00 00 00 r2 = 0 1: 7b 2a f8 ff 00 00 00 00 *(u64 *)(r10 - 8) = r2 2: b7 02 00 00 00 00 00 00 r2 = 0 3: b7 03 00 00 88 a2 00 00 r3 = 41608 4: 2d 23 03 00 00 00 00 00 if r3 > r2 goto +3 <LBB0_2> 5: b7 02 00 00 08 00 00 00 r2 = 8 6: 79 13 00 00 00 00 00 00 r3 = *(u64 *)(r1 + 0) 7: 05 00 02 00 00 00 00 00 goto +2 <LBB0_3> 0000000000000040 LBB0_2: 8: b7 02 00 00 08 00 00 00 r2 = 8 9: 79 13 08 00 00 00 00 00 r3 = *(u64 *)(r1 + 8) 0000000000000050 LBB0_3: 10: 0f 23 00 00 00 00 00 00 r3 += r2 11: bf a1 00 00 00 00 00 00 r1 = r10 12: 07 01 00 00 f8 ff ff ff r1 += -8 13: b7 02 00 00 08 00 00 00 r2 = 8 14: 85 00 00 00 04 00 00 00 call 4 Instructions #2, #5 and #8 need relocation resoutions from the loader. Signed-off-by: Yonghong Song <yhs@fb.com> Differential Revision: https://reviews.llvm.org/D61524 llvm-svn: 365503 |
|
Yonghong Song | 6db6b56a5c |
[BPF] Add BTF Var and DataSec Support
Two new kinds, BTF_KIND_VAR and BTF_KIND_DATASEC, are added. BTF_KIND_VAR has the following specification: btf_type.name: var name btf_type.info: type kind btf_type.type: var type // btf_type is followed by one u32 u32: varinfo (currently, only 0 - static, 1 - global allocated in elf sections) Not all globals are supported in this patch. The following globals are supported: . static variables with or without section attributes . global variables with section attributes The inclusion of globals with section attributes is for future potential extraction of key/value type id's from map definition. BTF_KIND_DATASEC has the following specification: btf_type.name: section name associated with variable or one of .data/.bss/.readonly btf_type.info: type kind and vlen for # of variables btf_type.size: 0 #vlen number of the following: u32: id of corresponding BTF_KIND_VAR u32: in-session offset of the var u32: the size of memory var occupied At the time of debug info emission, the data section size is unknown, so the btf_type.size = 0 for BTF_KIND_DATASEC. The loader can patch it during loading time. The in-session offseet of the var is only available for static variables. For global variables, the loader neeeds to assign the global variable symbol value in symbol table to in-section offset. The size of memory is used to specify the amount of the memory a variable occupies. Typically, it equals to the type size, but for certain structures, e.g., struct tt { int a; int b; char c[]; }; static volatile struct tt s2 = {3, 4, "abcdefghi"}; The static variable s2 has size of 20. Note that for BTF_KIND_DATASEC name, the section name does not contain object name. The compiler does have input module name. For example, two cases below: . clang -target bpf -O2 -g -c test.c The compiler knows the input file (module) is test.c and can generate sec name like test.data/test.bss etc. . clang -target bpf -O2 -g -emit-llvm -c test.c -o - | llc -march=bpf -filetype=obj -o test.o The llc compiler has the input file as stdin, and would generate something like stdin.data/stdin.bss etc. which does not really make sense. For any user specificed section name, e.g., static volatile int a __attribute__((section("id1"))); static volatile const int b __attribute__((section("id2"))); The DataSec with name "id1" and "id2" does not contain information whether the section is readonly or not. The loader needs to check the corresponding elf section flags for such information. A simple example: -bash-4.4$ cat t.c int g1; int g2 = 3; const int g3 = 4; static volatile int s1; struct tt { int a; int b; char c[]; }; static volatile struct tt s2 = {3, 4, "abcdefghi"}; static volatile const int s3 = 4; int m __attribute__((section("maps"), used)) = 4; int test() { return g1 + g2 + g3 + s1 + s2.a + s3 + m; } -bash-4.4$ clang -target bpf -O2 -g -S t.c Checking t.s, 4 BTF_KIND_VAR's are generated (s1, s2, s3 and m). 4 BTF_KIND_DATASEC's are generated with names ".data", ".bss", ".rodata" and "maps". Signed-off-by: Yonghong Song <yhs@fb.com> Differential Revision: https://reviews.llvm.org/D59441 llvm-svn: 356326 |
|
Chandler Carruth | 2946cd7010 |
Update the file headers across all of the LLVM projects in the monorepo
to reflect the new license. We understand that people may be surprised that we're moving the header entirely to discuss the new license. We checked this carefully with the Foundation's lawyer and we believe this is the correct approach. Essentially, all code in the project is now made available by the LLVM project under our new license, so you will see that the license headers include that license only. Some of our contributors have contributed code under our old license, and accordingly, we have retained a copy of our old license notice in the top-level files in each project and repository. llvm-svn: 351636 |
|
Yonghong Song | 7b410ac352 |
[BPF] Generate BTF DebugInfo under BPF target
This patch implements BTF (BPF Type Format).
The BTF is the debug info format for BPF, introduced
in the below linux patch:
|