Skip to content

Commit

Permalink
use .data.rel.ro segment for constant data with relocations
Browse files Browse the repository at this point in the history 
- The runtime linker will mark this as read only
  after relocations are processed.
  • Loading branch information
@MartinNowak
MartinNowak committed Feb 7, 2014
1 parent 1a99b8b commit 249844e
Show file tree
Hide file tree
Showing 3 changed files with 22 additions and 7 deletions.
1 change: 1 addition & 0 deletions src/backend/cdef.h
View file
Expand Up @@ -575,6 +575,7 @@ typedef targ_uns targ_size_t; /* size_t for the target machine */
#define DATA 2 /* initialized data */
#define CDATA 3 /* constant data */
#define UDATA 4 /* uninitialized data */
#define CDATAREL 5 /* constant data with relocs */
#define UNKNOWN -1 /* unknown segment */
#define DGROUPIDX 1 /* group index of DGROUP */

Expand Down
24 changes: 18 additions & 6 deletions src/backend/elfobj.c
View file
Expand Up @@ -227,6 +227,8 @@ static int section_cnt; // Number of sections in table
#define SHN_SECNAMES 9
#define SHN_COM 10
#define SHN_NOTE 11
#define SHN_GNUSTACK 12
#define SHN_CDATAREL 13

IDXSYM *mapsec2sym;
#define S2S_INC 20
Expand All @@ -244,6 +246,7 @@ static int local_cnt; // Number of symbols with STB_LOCAL
#define STI_RODAT 6 // Symbol for readonly data
#define STI_NOTE 7 // Where note symbol table entry is
#define STI_COM 8
#define STI_CDATAREL 9 // Symbol for readonly data with relocations

// NOTE: There seems to be a requirement that the read-only data have the
// same symbol table index and section index. Use section NOTE as a place
Expand Down Expand Up @@ -276,7 +279,7 @@ static const char compiler[] = "\0Digital Mars C/C++"
// same section as initialized data or code, so section offsets should
// be continuous when adding data. Fix-ups anywhere withing existing data.

#define COMD UDATA+1
#define COMD CDATAREL+1
#define OB_SEG_SIZ 10 // initial number of segments supported
#define OB_SEG_INC 10 // increment for additional segments

Expand Down Expand Up @@ -696,7 +699,7 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
if (I64)
{
static char section_names_init64[] =
"\0.symtab\0.strtab\0.shstrtab\0.text\0.data\0.bss\0.note\0.comment\0.rodata\0.note.GNU-stack\0.rela.text\0.rela.data";
"\0.symtab\0.strtab\0.shstrtab\0.text\0.data\0.bss\0.note\0.comment\0.rodata\0.note.GNU-stack\0.data.rel.ro\0.rela.text\0.rela.data";
#define NAMIDX_NONE 0
#define NAMIDX_SYMTAB 1 // .symtab
#define NAMIDX_STRTAB 9 // .strtab
Expand All @@ -708,9 +711,10 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
#define NAMIDX_COMMENT 50 // .comment
#define NAMIDX_RODATA 59 // .rodata
#define NAMIDX_GNUSTACK 67 // .note.GNU-stack
#define NAMIDX_RELTEXT 83 // .rel.text and .rela.text
#define NAMIDX_RELDATA 93 // .rel.data
#define NAMIDX_RELDATA64 94 // .rela.data
#define NAMIDX_CDATAREL 83 // .data.rel.ro
#define NAMIDX_RELTEXT 96 // .rel.text and .rela.text
#define NAMIDX_RELDATA 106 // .rel.data
#define NAMIDX_RELDATA64 107 // .rela.data

if (section_names)
section_names->setsize(sizeof(section_names_init64));
Expand Down Expand Up @@ -738,6 +742,7 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
elf_newsection2(NAMIDX_COMMENT, SHT_PROGDEF,0, 0,0,0,0,0, 1,0);
elf_newsection2(NAMIDX_NOTE,SHT_NOTE, 0, 0,0,0,0,0, 1,0);
elf_newsection2(NAMIDX_GNUSTACK,SHT_PROGDEF,0, 0,0,0,0,0, 1,0);
elf_newsection2(NAMIDX_CDATAREL,SHT_PROGDEF,SHF_ALLOC|SHF_WRITE,0,0,0,0,0, 16,0);

IDXSTR namidx;
namidx = NAMIDX_TEXT; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
Expand All @@ -752,11 +757,12 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
namidx = NAMIDX_COMMENT; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
namidx = NAMIDX_NOTE; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
namidx = NAMIDX_GNUSTACK; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
namidx = NAMIDX_CDATAREL; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
}
else
{
static char section_names_init[] =
"\0.symtab\0.strtab\0.shstrtab\0.text\0.data\0.bss\0.note\0.comment\0.rodata\0.note.GNU-stack\0.rel.text\0.rel.data";
"\0.symtab\0.strtab\0.shstrtab\0.text\0.data\0.bss\0.note\0.comment\0.rodata\0.note.GNU-stack\0.data.rel.ro\0.rel.text\0.rel.data";

if (section_names)
section_names->setsize(sizeof(section_names_init));
Expand Down Expand Up @@ -784,6 +790,7 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
elf_newsection2(NAMIDX_COMMENT, SHT_PROGDEF,0, 0,0,0,0,0, 1,0);
elf_newsection2(NAMIDX_NOTE,SHT_NOTE, 0, 0,0,0,0,0, 1,0);
elf_newsection2(NAMIDX_GNUSTACK,SHT_PROGDEF,0, 0,0,0,0,0, 1,0);
elf_newsection2(NAMIDX_CDATAREL,SHT_PROGDEF,SHF_ALLOC|SHF_WRITE,0,0,0,0,0, 1,0);

IDXSTR namidx;
namidx = NAMIDX_TEXT; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
Expand All @@ -798,6 +805,7 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
namidx = NAMIDX_COMMENT; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
namidx = NAMIDX_NOTE; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
namidx = NAMIDX_GNUSTACK; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
namidx = NAMIDX_CDATAREL; *(IDXSTR *)section_names_hashtable->get(&namidx) = namidx;
}

if (SYMbuf)
Expand All @@ -816,6 +824,7 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
elf_addsym(0, 0, 0, STT_SECTION, STB_LOCAL, SHN_RODAT); // STI_RODAT
elf_addsym(0, 0, 0, STT_SECTION, STB_LOCAL, SHN_NOTE); // STI_NOTE
elf_addsym(0, 0, 0, STT_SECTION, STB_LOCAL, SHN_COM); // STI_COM
elf_addsym(0, 0, 0, STT_SECTION, STB_LOCAL, SHN_CDATAREL); // STI_CDATAREL

// Initialize output buffers for CODE, DATA and COMMENTS
// (NOTE not supported, BSS not required)
Expand All @@ -834,6 +843,9 @@ Obj *Obj::init(Outbuffer *objbuf, const char *filename, const char *csegname)
elf_getsegment2(SHN_BSS, STI_BSS, 0);
assert(SegData[UDATA]->SDseg == UDATA);

elf_getsegment2(SHN_CDATAREL, STI_CDATAREL, 0);
assert(SegData[CDATAREL]->SDseg == CDATAREL);

elf_getsegment2(SHN_COM, STI_COM, 0);
assert(SegData[COMD]->SDseg == COMD);

Expand Down
4 changes: 3 additions & 1 deletion src/backend/out.c
View file
Expand Up @@ -519,7 +519,9 @@ void out_readonly(symbol *s)
* they require dynamic relocations of the read-only segment.
* Instead use the .data.rel.ro section. See Bugzilla 11171.
*/
if (!(config.flags3 & CFG3pic && dtpointers(s->Sdt)))
if (config.flags3 & CFG3pic && dtpointers(s->Sdt))
s->Sseg = CDATAREL;
else
s->Sseg = CDATA;
#endif
#if MACHOBJ
Expand Down

0 comments on commit 249844e

Please sign in to comment.