Date: Wed, 23 Oct 2019 19:03:03 +0000 (UTC) From: Conrad Meyer <cem@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r353959 - head/sys/amd64/include Message-ID: <201910231903.x9NJ33dI020909@repo.freebsd.org>
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Author: cem Date: Wed Oct 23 19:03:03 2019 New Revision: 353959 URL: https://svnweb.freebsd.org/changeset/base/353959 Log: amd64: Add CFI directives for libc syscall stubs No functional change (in program code). Additional DWARF metadata is generated in the .eh_frame section. Also, it is now a compile-time requirement that machine/asm.h ENTRY() and END() macros are paired. (This is subject to ongoing discussion and may change.) This DWARF metadata allows llvm-libunwind to unwind program stacks when the program is executing the function. The goal is to collect accurate userspace stacktraces when programs have entered syscalls. (The motivation for "Call Frame Information," or CFI for short -- not to be confused with Control Flow Integrity -- is to sufficiently annotate assembly functions such that stack unwinders can unwind out of the local frame without the requirement of a dedicated framepointer register; i.e., -fomit-frame-pointer. This is necessary for C++ exception handling or collecting backtraces.) For the curious, a more thorough description of the metadata and some examples may be found at [1] and documentation at [2]. You can also look at 'cc -S -o - foo.c | less' and search for '.cfi_' to see the CFI directives generated by your C compiler. [1]: https://www.imperialviolet.org/2017/01/18/cfi.html [2]: https://sourceware.org/binutils/docs/as/CFI-directives.html Reviewed by: emaste, kib (with reservations) Differential Revision: https://reviews.freebsd.org/D22122 Modified: head/sys/amd64/include/asm.h Modified: head/sys/amd64/include/asm.h ============================================================================== --- head/sys/amd64/include/asm.h Wed Oct 23 18:27:30 2019 (r353958) +++ head/sys/amd64/include/asm.h Wed Oct 23 19:03:03 2019 (r353959) @@ -60,25 +60,36 @@ #define _START_ENTRY .text; .p2align 4,0x90 #define _ENTRY(x) _START_ENTRY; \ - .globl CNAME(x); .type CNAME(x),@function; CNAME(x): + .globl CNAME(x); .type CNAME(x),@function; CNAME(x):; \ + .cfi_startproc #ifdef PROF #define ALTENTRY(x) _ENTRY(x); \ - pushq %rbp; movq %rsp,%rbp; \ + pushq %rbp; \ + .cfi_def_cfa_offset 16; \ + .cfi_offset %rbp, -16; \ + movq %rsp,%rbp; \ call PIC_PLT(HIDENAME(mcount)); \ popq %rbp; \ + .cfi_restore %rbp; \ + .cfi_def_cfa_offset 8; \ jmp 9f #define ENTRY(x) _ENTRY(x); \ - pushq %rbp; movq %rsp,%rbp; \ + pushq %rbp; \ + .cfi_def_cfa_offset 16; \ + .cfi_offset %rbp, -16; \ + movq %rsp,%rbp; \ call PIC_PLT(HIDENAME(mcount)); \ popq %rbp; \ + .cfi_restore %rbp; \ + .cfi_def_cfa_offset 8; \ 9: #else #define ALTENTRY(x) _ENTRY(x) #define ENTRY(x) _ENTRY(x) #endif -#define END(x) .size x, . - x +#define END(x) .size x, . - x; .cfi_endproc /* * WEAK_REFERENCE(): create a weak reference alias from sym. * The macro is not a general asm macro that takes arbitrary names,
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