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Message-Id: <20220823184157.42134-1-info@bnoordhuis.nl>
Date: Tue, 23 Aug 2022 20:41:57 +0200
From: Ben Noordhuis <info@...ordhuis.nl>
To: musl@...ts.openwall.com
Cc: Ben Noordhuis <info@...ordhuis.nl>
Subject: [PATCH] ldso: add basic ifunc support
Not perfect yet because it doesn't handle resolver functions that need
relocations themselves but basic functionality works. That is, this
works:
typedef void (*Func)(void);
void f(void) __attribute__((ifunc("g")));
Func g(void) { return h; }
void h(void) { abort(); }
But returning an extern function does not:
typedef void (*Func)(void);
void f(void) __attribute__((ifunc("g")));
Func g(void) { return abort; } // segfaults
---
arch/x86_64/reloc.h | 1 +
ldso/dynlink.c | 4 ++++
src/internal/dynlink.h | 1 +
3 files changed, 6 insertions(+)
diff --git a/arch/x86_64/reloc.h b/arch/x86_64/reloc.h
index fac0c0ae..fb6be3ea 100644
--- a/arch/x86_64/reloc.h
+++ b/arch/x86_64/reloc.h
@@ -10,6 +10,7 @@
#define REL_DTPOFF R_X86_64_DTPOFF64
#define REL_TPOFF R_X86_64_TPOFF64
#define REL_TLSDESC R_X86_64_TLSDESC
+#define REL_IRELATIVE R_X86_64_IRELATIVE
#define CRTJMP(pc,sp) __asm__ __volatile__( \
"mov %1,%%rsp ; jmp *%0" : : "r"(pc), "r"(sp) : "memory" )
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index fd09ca69..659cb113 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -507,6 +507,10 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
reloc_addr[1] = tmp;
#endif
break;
+ case REL_IRELATIVE:
+ *reloc_addr = (size_t)base + addend;
+ *reloc_addr = ((size_t(*)(void))*reloc_addr)();
+ break;
default:
error("Error relocating %s: unsupported relocation type %d",
dso->name, type);
diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
index 830354eb..c67bc35e 100644
--- a/src/internal/dynlink.h
+++ b/src/internal/dynlink.h
@@ -41,6 +41,7 @@ enum {
REL_TPOFF,
REL_TPOFF_NEG,
REL_TLSDESC,
+ REL_IRELATIVE,
REL_FUNCDESC,
REL_FUNCDESC_VAL,
};
--
2.34.1
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