Enable linking to a static position independent executable

Submitted by Harald Hoyer on April 27, 2020, 12:32 p.m.

Details

Message ID 20200427123207.1025966-1-harald@redhat.com
State New
Series "V2 Enable linking to a static position independent executable"
Headers show

Commit Message

Harald Hoyer April 27, 2020, 12:32 p.m.
From: Harald Hoyer <harald@redhat.com>

This also enables address space layout randomization (ASLR).

$ cat hello.c

int main()
{
  printf("main = 0x%lxd\n", main);
  return 0;
}

$ gcc -fPIE -static-pie -o hello hello.c -specs musl-gcc.specs

$ ldd hello
	statically linked

$ file hello
hello: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), statically linked, with debug_info, not stripped, too many notes (256)

$ ./hello
main = 0x7f858c4e72b9d

$ ./hello
main = 0x7f0854d312b9d

$ ./hello
main = 0x7f7179a1d2b9d

$ ./hello
main = 0x7f37f981b2b9d

$ readelf -l hello

Elf file type is DYN (Shared object file)
Entry point 0x104f
There are 7 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000308 0x0000000000000308  R      0x1000
  LOAD           0x0000000000001000 0x0000000000001000 0x0000000000001000
                 0x0000000000003eb7 0x0000000000003eb7  R E    0x1000
  LOAD           0x0000000000005000 0x0000000000005000 0x0000000000005000
                 0x000000000000136c 0x000000000000136c  R      0x1000
  LOAD           0x0000000000006e50 0x0000000000007e50 0x0000000000007e50
                 0x00000000000002e0 0x00000000000009a0  RW     0x1000
  DYNAMIC        0x0000000000006e70 0x0000000000007e70 0x0000000000007e70
                 0x0000000000000180 0x0000000000000180  RW     0x8
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x10
  GNU_RELRO      0x0000000000006e50 0x0000000000007e50 0x0000000000007e50
                 0x00000000000001b0 0x00000000000001b0  R      0x1

 Section to Segment mapping:
  Segment Sections...
   00     .hash .gnu.hash .dynsym .dynstr .rela.dyn
   01     .init .plt .text .fini
   02     .rodata .eh_frame
   03     .init_array .fini_array .data.rel.ro .dynamic .got .got.plt .data .bss
   04     .dynamic
   05
   06     .init_array .fini_array .data.rel.ro .dynamic .got
---
 tools/musl-gcc.specs.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
 mode change 100644 => 100755 tools/musl-gcc.specs.sh

Patch hide | download patch | download mbox

diff --git a/tools/musl-gcc.specs.sh b/tools/musl-gcc.specs.sh
old mode 100644
new mode 100755
index 30492574..ed584ed3
--- a/tools/musl-gcc.specs.sh
+++ b/tools/musl-gcc.specs.sh
@@ -17,13 +17,13 @@  cat <<EOF
 libgcc.a%s %:if-exists(libgcc_eh.a%s)
 
 *startfile:
-%{!shared: $libdir/Scrt1.o} $libdir/crti.o crtbeginS.o%s
+%{shared:;static-pie:$libdir/rcrt1.o; :$libdir/Scrt1.o} $libdir/crti.o crtbeginS.o%s
 
 *endfile:
 crtendS.o%s $libdir/crtn.o
 
 *link:
--dynamic-linker $ldso -nostdlib %{shared:-shared} %{static:-static} %{rdynamic:-export-dynamic}
+-dynamic-linker $ldso -nostdlib %{shared:-shared} %{static:-static} %{static-pie:-static -pie --no-dynamic-linker} %{rdynamic:-export-dynamic}
 
 *esp_link:
 

Comments

Harald Hoyer May 8, 2020, 9:05 a.m.
I think, that is as small and non invasive, as it can get.

> diff --git a/tools/musl-gcc.specs.sh b/tools/musl-gcc.specs.sh
> old mode 100644
> new mode 100755
> index 30492574..ed584ed3
> --- a/tools/musl-gcc.specs.sh
> +++ b/tools/musl-gcc.specs.sh
> @@ -17,13 +17,13 @@ cat <<EOF
>  libgcc.a%s %:if-exists(libgcc_eh.a%s)
>  
>  *startfile:
> -%{!shared: $libdir/Scrt1.o} $libdir/crti.o crtbeginS.o%s
> +%{shared:;static-pie:$libdir/rcrt1.o; :$libdir/Scrt1.o} $libdir/crti.o crtbeginS.o%s
>  
>  *endfile:
>  crtendS.o%s $libdir/crtn.o
>  
>  *link:
> --dynamic-linker $ldso -nostdlib %{shared:-shared} %{static:-static} %{rdynamic:-export-dynamic}
> +-dynamic-linker $ldso -nostdlib %{shared:-shared} %{static:-static} %{static-pie:-static -pie --no-dynamic-linker} %{rdynamic:-export-dynamic}
>  
>  *esp_link:
>  
>