Fix PLT creation for i386

i386 target does not have PC relative loads. Its ABI therefore require ebx register to points to the GOT when executing a PLT entry. This means that PLT entry cannot be used transparently, the compiler needs to expect execution of a PLT entry to be able to use one, that is a PLT entry should only be created if the relocation explicitely asks for it (eg. R_386_PLT32). This patch creates a new target macro PCRELATIVE_DLLPLT to indicate whether a target can do a PC relative load in PLT entry when building a dynamic library. Executable do not normally pose a problem because they are loaded at a fixed address and thus the absolute address of GOT can be used. Note that in such a case, if the compiler does not use a PLT aware relocation for external access then the code relocation will fall on the dynamic loader since there is no PLT entry to relocate too.

Thomas Preud'homme committed 9 years ago

Commit 0bf26281 parent e0fe6906 files · +16 −1Browse files

Unified · Split

6 files

arm-link.c +1 −0
arm64-link.c +1 −0
c67-link.c +1 −0
i386-link.c +1 −0
tccelf.c +11 −1
x86_64-link.c +1 −0

arm-link.c+1−0

@@ -15,6 +15,7 @@ · 14 unmodified lines
15	15	#define ELF_PAGE_SIZE 0x1000
16	16
17	17	#define HAVE_SECTION_RELOC
	18	+#define PCRELATIVE_DLLPLT 1
18	19
19	20	enum float_abi {
20	21	ARM_SOFTFP_FLOAT,

arm64-link.c+1−0

@@ -14,6 +14,7 @@ · 13 unmodified lines
14	14	#define ELF_PAGE_SIZE 0x1000
15	15
16	16	#define HAVE_SECTION_RELOC
	17	+#define PCRELATIVE_DLLPLT 1
17	18
18	19	#else /* !TARGET_DEFS_ONLY */
19	20

c67-link.c+1−0

@@ -15,6 +15,7 @@ · 14 unmodified lines
15	15	#define ELF_PAGE_SIZE 0x1000
16	16
17	17	#define HAVE_SECTION_RELOC
	18	+#define PCRELATIVE_DLLPLT 0
18	19
19	20	#else /* !TARGET_DEFS_ONLY */
20	21

i386-link.c+1−0

@@ -15,6 +15,7 @@ · 14 unmodified lines
15	15	#define ELF_PAGE_SIZE 0x1000
16	16
17	17	#define HAVE_SECTION_RELOC
	18	+#define PCRELATIVE_DLLPLT 0
18	19
19	20	#else /* !TARGET_DEFS_ONLY */
20	21

tccelf.c+11−1

@@ -1052,7 +1052,8 @@ ST_FUNC void build_got_entries(TCCState *s1) · 1051 unmodified lines
1052	1052	/* Proceed with PLT/GOT [entry] creation if any of the following
1053	1053	condition is met:
1054	1054	- it is an undefined reference (dynamic relocation needed)
1055		− - symbol is absolute (probably created by tcc_add_symbol)
	1055	+ - symbol is absolute (probably created by tcc_add_symbol and
	1056	+ thus might be too far from application code)
1056	1057	- relocation requires a PLT/GOT (BUILD_GOTPLT_ENTRY or
1057	1058	ALWAYS_GOTPLT_ENTRY). */
1058	1059	if (sym->st_shndx != SHN_UNDEF &&
@@ -1060,6 +1061,15 @@ ST_FUNC void build_got_entries(TCCState *s1) · 1 unmodified line
1060	1061	relocs_info[type].gotplt_entry == AUTO_GOTPLT_ENTRY)
1061	1062	continue;
1062	1063
	1064	+ /* Building a dynamic library but target is not capable of PC
	1065	+ relative PLT entries. It can thus only use PLT entries if
	1066	+ it expects one to be used (ALWAYS_GOTPLT_ENTRY). */
	1067	+ if (sym->st_shndx == SHN_UNDEF &&
	1068	+ s1->output_type == TCC_OUTPUT_DLL &&
	1069	+ !PCRELATIVE_DLLPLT &&
	1070	+ relocs_info[type].gotplt_entry == AUTO_GOTPLT_ENTRY)
	1071	+ continue;
	1072	+
1063	1073	#ifdef TCC_TARGET_X86_64
1064	1074	if (type == R_X86_64_PLT32 &&
1065	1075	ELFW(ST_VISIBILITY)(sym->st_other) != STV_DEFAULT) {

x86_64-link.c+1−0

@@ -15,6 +15,7 @@ · 14 unmodified lines
15	15	#define ELF_PAGE_SIZE 0x200000
16	16
17	17	#define HAVE_SECTION_RELOC
	18	+#define PCRELATIVE_DLLPLT 1
18	19
19	20	#else /* !TARGET_DEFS_ONLY */
20	21

Fix PLT creation for i386

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