tequilaOS/platform_bionic
2
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Add linker support for PIE

Browse source 
Modify the dynamic linker so that executables can be loaded
at locations other than 0x00000000.

Modify crtbegin* so that non-PIC compilant "thumb interwork
veneers" are not created by the linker.

Bug: 5323301
Change-Id: Iece0272e2b708c79034f302c20160e1fe9029588
This commit is contained in:
Nick Kralevich 2011-10-20 14:57:56 -07:00
parent b0641d4a44
commit d9ad62343c
3 changed files with 33 additions and 32 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
libc/arch-arm/bionic/crtbegin_dynamic.S
View file

@ -43,21 +43,17 @@
# - address of an "onexit" function, not used on any
# platform supported by Bionic
#
# - address of the "main" function of the program. We
# can't hard-code it in the adr pseudo instruction
# so we use a tiny trampoline that will get relocated
# by the dynamic linker before this code runs
# - address of the "main" function of the program.
#
# - address of the constructor list
#
_start:
mov r0, sp
mov r1, #0
adr r2, 0f
adr r3, 1f
b __libc_init
0: b main
ldr r2, =main
adr r3, 1f
ldr r4, =__libc_init
bx r4
1: .long __PREINIT_ARRAY__
.long __INIT_ARRAY__

14
libc/arch-arm/bionic/crtbegin_static.S
View file

@ -43,21 +43,17 @@
# - address of an "onexit" function, not used on any
# platform supported by Bionic
#
# - address of the "main" function of the program. We
# can't hard-code it in the adr pseudo instruction
# so we use a tiny trampoline that will get relocated
# by the dynamic linker before this code runs
# - address of the "main" function of the program.
#
# - address of the constructor list
#
_start:
mov r0, sp
mov r1, #0
adr r2, 0f
adr r3, 1f
b __libc_init
0: b main
ldr r2, =main
adr r3, 1f
ldr r4, =__libc_init
bx r4
1: .long __PREINIT_ARRAY__
.long __INIT_ARRAY__

37
linker/linker.c
View file

@ -1741,16 +1741,17 @@ static int link_image(soinfo *si, unsigned wr_offset)
if (phdr->p_type == PT_LOAD) {
/* For the executable, we use the si->size field only in
dl_unwind_find_exidx(), so the meaning of si->size
is not the size of the executable; it is the last
virtual address of the loadable part of the executable;
since si->base == 0 for an executable, we use the
range [0, si->size) to determine whether a PC value
falls within the executable section. Of course, if
a value is below phdr->p_vaddr, it's not in the
executable section, but a) we shouldn't be asking for
such a value anyway, and b) if we have to provide
an EXIDX for such a value, then the executable's
EXIDX is probably the better choice.
is not the size of the executable; it is the distance
between the load location of the executable and the last
address of the loadable part of the executable.
We use the range [si->base, si->base + si->size) to
determine whether a PC value falls within the executable
section. Of course, if a value is between si->base and
(si->base + phdr->p_vaddr), it's not in the executable
section, but a) we shouldn't be asking for such a value
anyway, and b) if we have to provide an EXIDX for such a
value, then the executable's EXIDX is probably the better
choice.
*/
DEBUG_DUMP_PHDR(phdr, "PT_LOAD", pid);
if (phdr->p_vaddr + phdr->p_memsz > si->size)
@ -1760,12 +1761,20 @@ static int link_image(soinfo *si, unsigned wr_offset)
if (!(phdr->p_flags & PF_W)) {
unsigned _end;
if (phdr->p_vaddr < si->wrprotect_start)
si->wrprotect_start = phdr->p_vaddr;
_end = (((phdr->p_vaddr + phdr->p_memsz + PAGE_SIZE - 1) &
if (si->base + phdr->p_vaddr < si->wrprotect_start)
si->wrprotect_start = si->base + phdr->p_vaddr;
_end = (((si->base + phdr->p_vaddr + phdr->p_memsz + PAGE_SIZE - 1) &
(~PAGE_MASK)));
if (_end > si->wrprotect_end)
si->wrprotect_end = _end;
/* Make the section writable just in case we'll have to
* write to it during relocation (i.e. text segment).
* However, we will remember what range of addresses
* should be write protected.
*/
mprotect((void *) (si->base + phdr->p_vaddr),
phdr->p_memsz,
PFLAGS_TO_PROT(phdr->p_flags) | PROT_WRITE);
}
} else if (phdr->p_type == PT_DYNAMIC) {
if (si->dynamic != (unsigned *)-1) {
@ -2183,7 +2192,7 @@ unsigned __linker_init(unsigned **elfdata)
vecs += 2;
}
si->base = 0;
si->base = (Elf32_Addr) si->phdr - si->phdr->p_vaddr;
si->dynamic = (unsigned *)-1;
si->wrprotect_start = 0xffffffff;
si->wrprotect_end = 0;