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[libc][setjmp] fix setjmp test via naked fn attr #88054

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Merged
merged 7 commits into from
Oct 15, 2024
Merged

[libc][setjmp] fix setjmp test via naked fn attr #88054

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7ffa468
[libc][setjmp] fix setjmp test
nickdesaulniers Apr 5, 2024
352824b
use naked attribute to implement setjmp
nickdesaulniers Apr 8, 2024
443e8aa
avoid __builtin_return_address
nickdesaulniers Apr 9, 2024
bc80aec
damned linter
nickdesaulniers Apr 9, 2024
7e1a505
use [[]] attribute syntax
nickdesaulniers Jun 20, 2024
0dec13e
remove omit frame pointer command line flags
nickdesaulniers Oct 10, 2024
734e044
use raw string literal
nickdesaulniers Oct 10, 2024
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6 changes: 0 additions & 6 deletions libc/src/setjmp/x86_64/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -8,12 +8,6 @@ add_entrypoint_object(
libc.hdr.types.jmp_buf
COMPILE_OPTIONS
-O3
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It seems weird to hardcode the optimization level, but that seems to be llvm-libc style so OK.

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Yes, I've discussed this with the team a bit. I'd prefer to "just do what libc++ does in terms of configuring the build for size vs performance." Looking at their docs it seems that CMAKE_BUILD_TYPE is perhaps the only way to signal that you'd like a release build, vs MinSizeRel.

Either way, we should file a new issue and discuss this there.

-fno-omit-frame-pointer
# TODO: Remove once one of these lands:
# https://github.com/llvm/llvm-project/pull/87837
# https://github.com/llvm/llvm-project/pull/88054
# https://github.com/llvm/llvm-project/pull/88157
-ftrivial-auto-var-init=uninitialized
)

add_entrypoint_object(
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60 changes: 24 additions & 36 deletions libc/src/setjmp/x86_64/setjmp.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
//
//===----------------------------------------------------------------------===//

#include "include/llvm-libc-macros/offsetof-macro.h"
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
#include "src/setjmp/setjmp_impl.h"
Expand All @@ -16,42 +17,29 @@

namespace LIBC_NAMESPACE_DECL {

LLVM_LIBC_FUNCTION(int, setjmp, (jmp_buf buf)) {
register __UINT64_TYPE__ rbx __asm__("rbx");
register __UINT64_TYPE__ r12 __asm__("r12");
register __UINT64_TYPE__ r13 __asm__("r13");
register __UINT64_TYPE__ r14 __asm__("r14");
register __UINT64_TYPE__ r15 __asm__("r15");

// We want to store the register values as is. So, we will suppress the
// compiler warnings about the uninitialized variables declared above.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->rbx) : "r"(rbx) :);
LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r12) : "r"(r12) :);
LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r13) : "r"(r13) :);
LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r14) : "r"(r14) :);
LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r15) : "r"(r15) :);
#pragma GCC diagnostic pop

// We want the rbp of the caller, which is what __builtin_frame_address(1)
// should return. But, compilers generate a warning that calling
// __builtin_frame_address with non-zero argument is unsafe. So, we use
// the knowledge of the x86_64 ABI to fetch the callers rbp. As per the ABI,
// the rbp of the caller is pushed on to the stack and then new top is saved
// in this function's rbp. So, we fetch it from location at which this
// functions's rbp is pointing.
buf->rbp = *reinterpret_cast<__UINTPTR_TYPE__ *>(__builtin_frame_address(0));

// The callers stack address is exactly 2 pointer widths ahead of the current
// frame pointer - between the current frame pointer and the rsp of the caller
// are the return address (pushed by the x86_64 call instruction) and the
// previous stack pointer as required by the x86_64 ABI.
// The stack pointer is ahead because the stack grows down on x86_64.
buf->rsp = reinterpret_cast<__UINTPTR_TYPE__>(__builtin_frame_address(0)) +
sizeof(__UINTPTR_TYPE__) * 2;
buf->rip = reinterpret_cast<__UINTPTR_TYPE__>(__builtin_return_address(0));
return 0;
[[gnu::naked]]
LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
asm(R"(
mov %%rbx, %c[rbx](%%rdi)
mov %%rbp, %c[rbp](%%rdi)
mov %%r12, %c[r12](%%rdi)
mov %%r13, %c[r13](%%rdi)
mov %%r14, %c[r14](%%rdi)
mov %%r15, %c[r15](%%rdi)

lea 8(%%rsp), %%rax
mov %%rax, %c[rsp](%%rdi)

mov (%%rsp), %%rax
mov %%rax, %c[rip](%%rdi)

xorl %%eax, %%eax
retq)" ::[rbx] "i"(offsetof(__jmp_buf, rbx)),
[rbp] "i"(offsetof(__jmp_buf, rbp)), [r12] "i"(offsetof(__jmp_buf, r12)),
[r13] "i"(offsetof(__jmp_buf, r13)), [r14] "i"(offsetof(__jmp_buf, r14)),
[r15] "i"(offsetof(__jmp_buf, r15)), [rsp] "i"(offsetof(__jmp_buf, rsp)),
[rip] "i"(offsetof(__jmp_buf, rip))
: "rax");
}

} // namespace LIBC_NAMESPACE_DECL
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