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Merge pull request #1309 from Yawning/fix/freebsd-syscall

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src: "Fix" the system call intrinsic for FreeBSD
This commit is contained in:
gingerBill
2023-06-07 12:04:57 +01:00
committed by GitHub
parent 8441c0c51e 02a8bba02e
commit 151396507e
1 changed files with 45 additions and 4 deletions
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src/llvm_backend_proc.cpp
+45 -4
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@@ -2660,10 +2660,26 @@ gb_internal lbValue lb_build_builtin_proc(lbProcedure *p, Ast *expr, TypeAndValu
{
GB_ASSERT(arg_count <= 7);
// FreeBSD additionally clobbers r8, r9, r10, but they
// can also be used to pass in arguments, so this needs
// to be handled in two parts.
bool clobber_arg_regs[7] = {
false, false, false, false, false, false, false
};
if (build_context.metrics.os == TargetOs_freebsd) {
clobber_arg_regs[4] = true; // r10
clobber_arg_regs[5] = true; // r8
clobber_arg_regs[6] = true; // r9
}
char asm_string[] = "syscall";
gbString constraints = gb_string_make(heap_allocator(), "={rax}");
for (unsigned i = 0; i < arg_count; i++) {
constraints = gb_string_appendc(constraints, ",{");
if (!clobber_arg_regs[i]) {
constraints = gb_string_appendc(constraints, ",{");
} else {
constraints = gb_string_appendc(constraints, ",+{");
}
static char const *regs[] = {
"rax",
"rdi",
@@ -2687,10 +2703,35 @@ gb_internal lbValue lb_build_builtin_proc(lbProcedure *p, Ast *expr, TypeAndValu
// Some but not all system calls will additionally
// clobber memory.
//
// TODO: FreeBSD is different and will also clobber
// R8, R9, and R10. Additionally CF is used to
// indicate an error instead of -errno.
// As a fix for CVE-2019-5595, FreeBSD started
// clobbering R8, R9, and R10, instead of restoring
// them. Additionally unlike Linux, instead of
// returning negative errno, positive errno is
// returned and CF is set.
//
// TODO:
// * Figure out what Darwin does.
// * Add some extra handling to propagate CF back
// up to the caller on FreeBSD systems so that
// the caller knows that the return value is
// positive errno.
constraints = gb_string_appendc(constraints, ",~{rcx},~{r11},~{memory}");
if (build_context.metrics.os == TargetOs_freebsd) {
// Second half of dealing with FreeBSD's system
// call semantics. Explicitly clobber the registers
// that were not used to pass in arguments, and
// then clobber RFLAGS.
if (arg_count < 5) {
constraints = gb_string_appendc(constraints, ",~{r10}");
}
if (arg_count < 6) {
constraints = gb_string_appendc(constraints, ",~{r8}");
}
if (arg_count < 7) {
constraints = gb_string_appendc(constraints, ",~{r9}");
}
constraints = gb_string_appendc(constraints, ",~{cc}");
}
inline_asm = llvm_get_inline_asm(func_type, make_string_c(asm_string), make_string_c(constraints));
}