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Get --ftrace working on aarch64

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This change implements a new approach to function call logging, that's
based on the GCC flag: -fpatchable-function-entry. Read the commentary
in build/config.mk to learn how it works.
This commit is contained in:
Justine Tunney 2023-06-05 23:35:31 -07:00
parent 5b908bc756
commit eb40cb371d
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GPG key ID: BE714B4575D6E328
934 changed files with 2259 additions and 1268 deletions
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50
tool/build/fixupobj.c
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@ -54,6 +54,17 @@ Usage: fixupobj.com [-h] ARGS...\n\
#define MRS_TPIDR_EL0 0xd53bd040u
#define MOV_REG(DST, SRC) (0xaa0003e0u | (SRC) << 16 | (DST))
static const unsigned char kFatNops[8][8] = {
{}, //
{0x90}, // nop
{0x66, 0x90}, // xchg %ax,%ax
{0x0f, 0x1f, 0x00}, // nopl (%rax)
{0x0f, 0x1f, 0x40, 0x00}, // nopl 0x00(%rax)
{0x0f, 0x1f, 0x44, 0x00, 0x00}, // nopl 0x00(%rax,%rax,1)
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, // nopw 0x00(%rax,%rax,1)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, // nopl 0x00000000(%rax)
};
void Write(const char *s, ...) {
va_list va;
va_start(va, s);
@ -110,6 +121,44 @@ void RewriteTlsCode(Elf64_Ehdr *elf, size_t elfsize) {
}
}
/**
* Improve GCC11 `-fpatchable-function-entry` codegen.
*
* When using flags like `-fpatchable-function-entry=9,7` GCC v11 will
* insert two `nop` instructions, rather than merging them into faster
* "fat" nops.
*
* In order for this to work, the function symbol must be declared as
* `STT_FUNC` and `st_size` must have the function's byte length.
*/
void OptimizePatchableFunctionEntries(Elf64_Ehdr *elf, size_t elfsize) {
#ifdef __x86_64__
long i, n;
int nopcount;
Elf64_Sym *syms;
Elf64_Shdr *shdr;
Elf64_Xword symcount;
unsigned char *p, *pe;
CHECK_NOTNULL((syms = GetElfSymbolTable(elf, elfsize, &symcount)));
for (i = 0; i < symcount; ++i) {
if (ELF64_ST_TYPE(syms[i].st_info) == STT_FUNC && syms[i].st_size) {
shdr = GetElfSectionHeaderAddress(elf, elfsize, syms[i].st_shndx);
p = GetElfSectionAddress(elf, elfsize, shdr);
p += syms[i].st_value;
pe = p + syms[i].st_size;
for (; p + 1 < pe; p += n) {
if (p[0] != 0x90) break;
if (p[1] != 0x90) break;
for (n = 2; p + n < pe && n < ARRAYLEN(kFatNops); ++n) {
if (p[n] != 0x90) break;
}
memcpy(p, kFatNops[n], n);
}
}
}
#endif /* __x86_64__ */
}
void OptimizeRelocations(Elf64_Ehdr *elf, size_t elfsize) {
char *strs;
Elf64_Half i;
@ -191,6 +240,7 @@ void RewriteObject(const char *path) {
}
if (elf->e_machine == EM_NEXGEN32E) {
OptimizeRelocations(elf, st.st_size);
OptimizePatchableFunctionEntries(elf, st.st_size);
}
if (elf->e_machine == EM_AARCH64) {
RewriteTlsCode(elf, st.st_size);