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From: Fangrui Song <i@maskray.me>
To: harald@redhat.com
Cc: musl@lists.openwall.com
Subject: Re: [musl] [PATCH] V2 Enable linking to a static position independent executable
Date: Mon, 6 Apr 2020 15:04:03 -0700	[thread overview]
Message-ID: <20200406220403.3moghw2llo34e6gh@gmail.com> (raw)
In-Reply-To: <20200406180738.946894-1-harald@redhat.com>

On 2020-04-06, harald@redhat.com wrote:
>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(-)
> mode change 100644 => 100755 tools/musl-gcc.specs.sh
>
>diff --git a/tools/musl-gcc.specs.sh b/tools/musl-gcc.specs.sh
>old mode 100644
>new mode 100755
>index 30492574..72f5f487
>--- 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

The intention of the compiler driver option -static-pie is that it only
affects linking options (-static -pie --no-dynamic-linker -z text), not compile options (-fPIE).

(I don't know why -z text (which is not too relevant) ended up in GCC's default specs.
  Anyway, I followed suit for clang: https://reviews.llvm.org/D62606)

> *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 %{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:
>
>-- 
>2.25.2
>

  reply	other threads:[~2020-04-06 22:04 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-06 18:07 harald
2020-04-06 22:04 ` Fangrui Song [this message]
2020-04-07  8:42   ` Szabolcs Nagy
2020-04-07 13:17   ` [musl] [PATCH] " harald
2020-04-23 11:59     ` Harald Hoyer
2020-04-24 15:08     ` Rich Felker
2020-04-27 12:24       ` Harald Hoyer
2020-04-27 12:32         ` harald
2020-05-08  9:05           ` Harald Hoyer
2020-08-25 10:52           ` Harald Hoyer

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