Le mardi 6 novembre 2012 16:37:21, Thomas Preud'homme a écrit : > Le mardi 6 novembre 2012 16:22:00, Milutin Jovanović a écrit :
> Sure, I agree I don't like it. It create a risk of forgetting it for the > future. But accessors or bitfield doesn't change anything. Bitfield needs > to shift the value to the left for each use and accessors need to be used > for each case. Someone reading tcc.h will be tempted to use the field > immediately. At least bitfield makes it more clear to the compiler what's > going on but it will not catch a mistake such has reading the value > directly from got_offset. I went with bit fields in the end. I also modified put_got_offset so that a value can be set twice. Although it's not needed now, put_got_offset could be used by someone in this way later on and that would lead to subtle bugs. > > Small stylistic issue is that I (personally) don't like '& -2' mask. I > > think this obfuscates the intent, and the simple '& ~1' is more usual, > > and it should not be any slower. -2 also assumes two's complement > > implementations... Hence gone :) I'll appreciate another review if you have time. Thanks again. Thomas
diff --git a/tcc.h b/tcc.h
index 4e88782..e81e89c 100644
--- a/tcc.h
+++ b/tcc.h
@@ -33,6 +33,7 @@
#include <stdlib.h>
#include <stdio.h>
+#include <limits.h>
#include <stdarg.h>
#include <string.h>
#include <errno.h>
@@ -524,11 +525,14 @@ struct TCCState {
Section **priv_sections;
int nb_priv_sections; /* number of private sections */
- /* got handling */
+ /* got & plt handling */
Section *got;
Section *plt;
- unsigned long *got_offsets;
- int nb_got_offsets;
+ struct {
+ unsigned long plt_thumb_stub:1;
+ unsigned long got_offset:(sizeof(long)*CHAR_BIT-1);
+ } *sym_infos;
+ int nb_sym_infos;
/* give the correspondance from symtab indexes to dynsym indexes */
int *symtab_to_dynsym;
diff --git a/tccelf.c b/tccelf.c
index d0e4c3b..9b3fa2d 100644
--- a/tccelf.c
+++ b/tccelf.c
@@ -581,7 +581,7 @@ ST_FUNC void relocate_section(TCCState *s1, Section *s)
break;
case R_386_GOT32:
/* we load the got offset */
- *(int *)ptr += s1->got_offsets[sym_index];
+ *(int *)ptr += s1->sym_infos[sym_index].got_offset << 1;
break;
case R_386_16:
if (s1->output_format != TCC_OUTPUT_FORMAT_BINARY) {
@@ -758,7 +758,7 @@ ST_FUNC void relocate_section(TCCState *s1, Section *s)
break;
case R_ARM_GOT_BREL:
/* we load the got offset */
- *(int *)ptr += s1->got_offsets[sym_index];
+ *(int *)ptr += s1->sym_infos[sym_index].got_offset << 1;
break;
case R_ARM_COPY:
break;
@@ -864,14 +864,14 @@ ST_FUNC void relocate_section(TCCState *s1, Section *s)
}
#endif
*(int *)ptr += (s1->got->sh_addr - addr +
- s1->got_offsets[sym_index] - 4);
+ (s1->sym_infos[sym_index].got_offset << 1) - 4);
break;
case R_X86_64_GOTTPOFF:
*(int *)ptr += val - s1->got->sh_addr;
break;
case R_X86_64_GOT32:
/* we load the got offset */
- *(int *)ptr += s1->got_offsets[sym_index];
+ *(int *)ptr += s1->sym_infos[sym_index].got_offset << 1;
break;
#else
#error unsupported processor
@@ -941,23 +941,36 @@ static int prepare_dynamic_rel(TCCState *s1, Section *sr)
return count;
}
-static void put_got_offset(TCCState *s1, int index, unsigned long val)
+static void put_sym_info(TCCState *s1, int index)
{
int n;
- unsigned long *tab;
+ typeof(s1->sym_infos) tab;
- if (index >= s1->nb_got_offsets) {
+ if (index >= s1->nb_sym_infos) {
/* find immediately bigger power of 2 and reallocate array */
n = 1;
while (index >= n)
n *= 2;
- tab = tcc_realloc(s1->got_offsets, n * sizeof(unsigned long));
- s1->got_offsets = tab;
- memset(s1->got_offsets + s1->nb_got_offsets, 0,
- (n - s1->nb_got_offsets) * sizeof(unsigned long));
- s1->nb_got_offsets = n;
+ tab = tcc_realloc(s1->sym_infos, n * sizeof(unsigned long));
+ s1->sym_infos = tab;
+ memset(s1->sym_infos + s1->nb_sym_infos, 0,
+ (n - s1->nb_sym_infos) * sizeof(unsigned long));
+ s1->nb_sym_infos = n;
}
- s1->got_offsets[index] = val;
+}
+
+#ifdef TCC_TARGET_ARM
+static void put_plt_thumb_stub(TCCState *s1, int index, unsigned char bit)
+{
+ put_sym_info(s1, index);
+ s1->sym_infos[index].plt_thumb_stub = bit;
+}
+#endif
+
+static void put_got_offset(TCCState *s1, int index, unsigned long val)
+{
+ put_sym_info(s1, index);
+ s1->sym_infos[index].got_offset = val >> 1;
}
/* XXX: suppress that */
@@ -1021,8 +1034,8 @@ static void put_got_entry(TCCState *s1,
build_got(s1);
/* if a got entry already exists for that symbol, no need to add one */
- if (sym_index < s1->nb_got_offsets &&
- s1->got_offsets[sym_index] != 0)
+ if (sym_index < s1->nb_sym_infos &&
+ s1->sym_infos[sym_index].got_offset << 1)
return;
put_got_offset(s1, sym_index, s1->got->data_offset);
@@ -1102,10 +1115,13 @@ static void put_got_entry(TCCState *s1,
put32(p + 12, 0xe5bef008);
}
- p = section_ptr_add(plt, 20);
- put32(p , 0x4778); // bx pc
- put32(p+2, 0x46c0); // nop
- p += 4;
+ if (s1->sym_infos[sym_index].plt_thumb_stuff) {
+ p = section_ptr_add(plt, 20);
+ put32(p , 0x4778); // bx pc
+ put32(p+2, 0x46c0); // nop
+ p += 4;
+ } else
+ p = section_ptr_add(plt, 16);
put32(p , 0xe59fc004); // ldr ip, [pc, #4] // offset in GOT
put32(p+4, 0xe08fc00c); // add ip, pc, ip // absolute address or offset
put32(p+8, 0xe59cf000); // ldr pc, [ip] // load absolute address or load offset
@@ -1492,9 +1508,9 @@ ST_FUNC void fill_got_entry(TCCState *s1, ElfW_Rel *rel)
ElfW(Sym) *sym = &((ElfW(Sym) *) symtab_section->data)[sym_index];
unsigned long offset;
- if (sym_index >= s1->nb_got_offsets)
+ if (sym_index >= s1->nb_sym_infos)
return;
- offset = s1->got_offsets[sym_index];
+ offset = s1->sym_infos[sym_index].got_offset << 1;
section_reserve(s1->got, offset + PTR_SIZE);
#ifdef TCC_TARGET_X86_64
/* only works for x86-64 */
@@ -2068,7 +2084,8 @@ static int elf_output_file(TCCState *s1, const char *filename)
x=s1->got->sh_addr - s1->plt->sh_addr - 12;
p += 16;
while (p < p_end) {
- p += 4;
+ if (get32(p) == 0x46c04778) /* PLT Thumb stub present */
+ p += 4;
put32(p + 12, x + get32(p + 12) + s1->plt->data - p);
p += 16;
}
@@ -2302,7 +2319,7 @@ static int elf_output_file(TCCState *s1, const char *filename)
tcc_free(s1->symtab_to_dynsym);
tcc_free(section_order);
tcc_free(phdr);
- tcc_free(s1->got_offsets);
+ tcc_free(s1->sym_infos);
return ret;
}
@@ -2597,6 +2614,19 @@ ST_FUNC int tcc_load_object_file(TCCState *s1,
rel->r_info = ELFW(R_INFO)(sym_index, type);
/* offset the relocation offset */
rel->r_offset += offseti;
+#ifdef TCC_TARGET_ARM
+ /* Jumps and branches from a Thumb code to a PLT entry need
+ special handling since PLT entries are ARM code.
+ Unconditional bl instructions referencing PLT entries are
+ handled by converting these instructions into blx
+ instructions. Other case of instructions referencing a PLT
+ entry require to add a Thumb stub before the PLT entry to
+ switch to ARM mode. We set bit 0 of the got offset of a
+ symbol to indicate such a case. */
+ if (type == R_ARM_THM_JUMP24) {
+ put_plt_thumb_stub(s1, sym_index, 1);
+ }
+#endif
}
break;
default:
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