[PATCH v1] ld/ELF: Add --image-base command line option to the ELF linker

[Hakan Candar]

Dear Alan Modra,

Sorry for the second mail. I forgot to CC the mailing list.

I am in the process of writing an updated patch, I fixed tests for all
targets except nds32le-linux-gnu, arc-linux-uclibc, and
h8300-linux-gnu.

Only on targets nds32le-linux-gnu and arc-linux-uclibc, the paddr and
vaddr of the data segment is different. I suspect this might be a bug.

Readelf output:
Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  LOAD           0x000000 0x00120000 0x00110000 0x00094 0x00094 R   0x10000
  LOAD           0x000094 0x00120094 0x00120094 0x00002 0x00002 R E 0x10000
  LOAD           0x000098 0x00130098 0x00130098 0x00000 0x00000 RW  0x10000

Notice how the VirtAddr and PhysAddr of the first segment is different.
This behaviour is always present, regardless if -Ttext-segment was
specified or not.

I can fix the issue by changing the ldscripts of those two targets and
adding `. = ALIGN(CONSTANT (MAXPAGESIZE));` over `.init` for
SEPARATE_CODE, similar to how other targets handle this. After this
is done, these targets behave like other platforms where paddr and
vaddr is the same.

How may I continue? Should I change the test case from
"  LOAD +0x0+ 0x0*120000 0x0*120000 0x[0-9a-f]+ 0x[0-9a-f]+ R   .*"
to
"  LOAD +0x0+ 0x0*120000 0x[0-9a-f]+ 0x[0-9a-f]+ 0x[0-9a-f]+ R   .*"
not accounting for the physical address, or should the test stay as is
and a new bug report be opened for this problem?

Further, the h8300-linux-gnu target did not create two different
segments (R) and (RX) when -z separate-code was specified. It acted as
-z noseparate-code. I am thinking of adding this target as xfail.

Best regards,
Hakan

On Friday, 25 October 2024 at 06:37, Alan Modra <amodra@gmail.com> wrote:

> On Fri, Oct 25, 2024 at 01:25:21AM +0000, hakan wrote:
> 
> > LLD has dropped the option -Ttext-segment for specifying image base
> > addresses, instead forcing the use of the --image-base option for both
> > ELF and PE targets. As it stands, GNU LD and LLVM LLD are incompatible,
> > having two different options for the same functionality.
> > 
> > This patch enables the use of --image-base on ELF targets, advancing
> > consistency and compatibility.
> > 
> > See: https://reviews.llvm.org/D70468
> > https://maskray.me/blog/2020-11-15-explain-gnu-linker-options#address-related
> > https://sourceware.org/bugzilla/show_bug.cgi?id=25207
> > 
> > Moreover, a new test has been added to ensure -z separate-code behaviour
> > when used with -Ttext-segment stays the same. When this combination is
> > used, -Ttext-segment sets the address of the first segment (R), not the
> > text segment (RX), and like with -z noseparate-code, no segments lesser
> > than the specified address are created. If this behaviour was to change,
> > the first (R) segment of the ELF file would begin in a lesser address
> > than the specified text (RX) segment, breaking traditional use of this
> > option for specifying image base address.
> > 
> > ld/
> > PR 25207
> > * emultempl/pe.em: Remove redeclaration of --image-base.
> > * emultempl/pep.em: Ditto.
> > * emultempl/beos.em: Ditto.
> > * ldlex.h (enum option_values): Move OPTION_IMAGE_BASE.
> > * lexsup.c (ld_options): Add --image-base.
> > (parse_args): On ELF, make --image-base follow -Ttext-segment behaviour.
> > * ld.texi: Document the new option and re-define -Ttext-segment
> > with established behaviour.
> > * testsuite/ld-elf/pr25207.d: New file.
> > * testsuite/ld-elf/pr25207.s: New file.
> > * NEWS: Mention the new feature.
> > 
> > Tested on Linux x86-64, for ELF and PE targets.
> 
> 
> The test needs some tweaking. Fix these fails then the patch is OK.
> 
> arc-linux-uclibc +FAIL: ld-elf/pr25207
> bfin-linux-uclibc +FAIL: ld-elf/pr25207
> h8300-linux-gnu +FAIL: ld-elf/pr25207
> hppa64-linux-gnu +FAIL: ld-elf/pr25207
> metag-linux-gnu +FAIL: ld-elf/pr25207
> mips64-linux-gnuabi64 +FAIL: ld-elf/pr25207
> mipsel-linux-gnu +FAIL: ld-elf/pr25207
> mipsisa32el-linux-gnu +FAIL: ld-elf/pr25207
> mips-linux-gnu +FAIL: ld-elf/pr25207
> nds32le-linux-gnu +FAIL: ld-elf/pr25207
> sparc64-linux-gnu +FAIL: ld-elf/pr25207
> 
> --
> Alan Modra