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Add an implementation of .mcount on arm64

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To support cc -pg on arm64 we need to implement .mcount. As clang and
gcc think it is function like it just needs to load the arguments
to _mcount and call it.

On gcc the first argument is passed in x0, however this is missing on
clang so we need to load it from the stack. As it's the caller return
address this will be at a known location.

PR:		262709
Reviewed by:	emaste (earlier version)
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34634
This commit is contained in:
Andrew Turner 2022-03-22 15:46:15 +00:00
parent f9413897cb
commit 16d5f9a164
2 changed files with 45 additions and 1 deletions
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1
lib/libc/aarch64/Symbol.map
View File

@ -11,6 +11,7 @@ FBSD_1.0 {
/* PSEUDO syscalls */
_exit;
.mcount;
_setjmp;
_longjmp;
fabs;

45
sys/arm64/include/profile.h
View File

@ -44,8 +44,51 @@ typedef u_long fptrdiff_t;
typedef __uintfptr_t uintfptr_t;
#define _MCOUNT_DECL void mcount
#define _MCOUNT_DECL \
static void _mcount(uintfptr_t frompc, uintfptr_t selfpc) __used; \
static void _mcount
#ifdef __GNUCLIKE_ASM
/*
* Call into _mcount. On arm64 the .mcount is a function so callers will
* handle caller saved registers. As we don't directly touch any callee
* saved registers we can just load the two arguments and use a tail call
* into the MI _mcount function.
*
* When building with gcc frompc will be in x0, however this is not the
* case on clang. As such we need to load it from the stack. As long as
* the caller follows the ABI this will load the correct value.
*/
#define MCOUNT __asm( \
" .text \n" \
" .align 6 \n" \
" .type .mcount,#function \n" \
" .globl .mcount \n" \
" .mcount: \n" \
" .cfi_startproc \n" \
/* Load the caller return address as frompc */ \
" ldr x0, [x29, #8] \n" \
/* Use our return address as selfpc */ \
" mov x1, lr \n" \
" b _mcount \n" \
" .cfi_endproc \n" \
" .size .mcount, . - .mcount \n" \
);
#if 0
/*
* If clang passed frompc correctly we could implement it like this, however
* all clang versions we care about would need to be fixed before we could
* make this change.
*/
void
mcount(uintfptr_t frompc)
{
_mcount(frompc, __builtin_return_address(0));
}
#endif
#else
#define MCOUNT
#endif
#endif /* !_KERNEL */