[musl] [PATCH] Enable linking to a static position independent executable

[harald@redhat.com]

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 -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, BuildID[sha1]=24fe0d02b0558dc37b8ae2268878b118804ae72d, with debug_info, not stripped

$ ./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 0x1058
There are 9 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x00000000000003c0 0x00000000000003c0  R      0x1000
  LOAD           0x0000000000001000 0x0000000000001000 0x0000000000001000
                 0x0000000000002cce 0x0000000000002cce  R E    0x1000
  LOAD           0x0000000000004000 0x0000000000004000 0x0000000000004000
                 0x0000000000001550 0x0000000000001550  R      0x1000
  LOAD           0x0000000000005e50 0x0000000000006e50 0x0000000000006e50
                 0x00000000000002e0 0x00000000000009a0  RW     0x1000
  DYNAMIC        0x0000000000005e70 0x0000000000006e70 0x0000000000006e70
                 0x0000000000000170 0x0000000000000170  RW     0x8
  NOTE           0x0000000000000238 0x0000000000000238 0x0000000000000238
                 0x0000000000000024 0x0000000000000024  R      0x4
  GNU_EH_FRAME   0x0000000000004b60 0x0000000000004b60 0x0000000000004b60
                 0x00000000000001ec 0x00000000000001ec  R      0x4
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x10
  GNU_RELRO      0x0000000000005e50 0x0000000000006e50 0x0000000000006e50
                 0x00000000000001b0 0x00000000000001b0  R      0x1

 Section to Segment mapping:
  Segment Sections...
   00     .note.gnu.build-id .gnu.hash .dynsym .dynstr .rela.dyn
   01     .init .plt .text .fini
   02     .rodata .eh_frame_hdr .eh_frame
   03     .init_array .fini_array .data.rel.ro .dynamic .got .got.plt .data .bss
   04     .dynamic
   05     .note.gnu.build-id
   06     .eh_frame_hdr
   07
   08     .init_array .fini_array .data.rel.ro .dynamic .got
---
 tools/musl-gcc.specs.sh | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/musl-gcc.specs.sh b/tools/musl-gcc.specs.sh
index 30492574..7e7ae562 100644
--- a/tools/musl-gcc.specs.sh
+++ b/tools/musl-gcc.specs.sh
@@ -8,7 +8,7 @@ cat <<EOF
 -nostdinc -isystem $incdir -isystem include%s %(old_cpp_options)
 
 *cc1:
-%(cc1_cpu) -nostdinc -isystem $incdir -isystem include%s
+%(cc1_cpu) %{static-pie:-fPIE} -nostdinc -isystem $incdir -isystem include%s
 
 *link_libgcc:
 -L$libdir -L .%s
@@ -17,13 +17,13 @@ cat <<EOF
 libgcc.a%s %:if-exists(libgcc_eh.a%s)
 
 *startfile:
-%{!shared: $libdir/Scrt1.o} $libdir/crti.o crtbeginS.o%s
+%{shared:;static:$libdir/crt1.o%s; static-pie:$libdir/rcrt1.o%s; pie:$libdir/Scrt1.o%s; :$libdir/crt1.o%s} $libdir/crti.o%s %{static:crtbeginT.o%s; shared|static-pie|pie:crtbeginS.o%s; :crtbegin.o%s}
 
 *endfile:
-crtendS.o%s $libdir/crtn.o
+%{static:crtend.o%s; shared|static-pie|pie:crtendS.o%s; :crtend.o%s} $libdir/crtn.o%s
 
 *link:
--dynamic-linker $ldso -nostdlib %{shared:-shared} %{static:-static} %{rdynamic:-export-dynamic}
+%{!r:--build-id} --no-add-needed %{!static|static-pie:--eh-frame-hdr} --hash-style=gnu -m elf_x86_64 %{shared:-shared} %{!shared:%{!static:%{!static-pie:%{rdynamic:-export-dynamic} -dynamic-linker $ldso}} %{static:-static} %{static-pie:-static -pie --no-dynamic-linker -z text}}
 
 *esp_link:
 
-- 
2.26.0