Add linker support for PIE
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
diff --git a/libc/arch-arm/bionic/crtbegin_dynamic.S b/libc/arch-arm/bionic/crtbegin_dynamic.S
index 0999084..6ca0845 100644
--- a/libc/arch-arm/bionic/crtbegin_dynamic.S
+++ b/libc/arch-arm/bionic/crtbegin_dynamic.S
@@ -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__
diff --git a/libc/arch-arm/bionic/crtbegin_static.S b/libc/arch-arm/bionic/crtbegin_static.S
index 13b05b2..e62ac1d 100644
--- a/libc/arch-arm/bionic/crtbegin_static.S
+++ b/libc/arch-arm/bionic/crtbegin_static.S
@@ -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__
diff --git a/linker/linker.c b/linker/linker.c
index bcfa8dc..a71986d 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -1650,16 +1650,17 @@
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)
@@ -1669,12 +1670,20 @@
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) {
@@ -2069,7 +2078,7 @@
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;
