[Bug ld/31795] ld.bfd makes ELFs of type ET_EXEC for static PIEs when load address is non-0

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31795

--- Comment #23 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to mintsuki from comment #21)
> (In reply to H.J. Lu from comment #20)
> > It turns out that static PIE with non-zero load address must have ET_EXEC:
> > 
> > https://sourceware.org/bugzilla/show_bug.cgi?id=31799
> > 
> > Otherwise, there is no way for loader to tell if the dynamic section entries
> > contain the relocated values for the load address or not.  Since static PIE
> > with non-zero load address must have ET_EXEC, PIE with non-zero load address
> > also should have ET_EXEC.
> > 
> > BTW, gold doesn't support static PIE and static PIE with non-zero load
> > address
> > generated by lld crashes with the fix glibc.
> 
> At least in the context of making a kernel, gold does generate a static-pie,
> at least as printed out by the file command, and the output of readelf -a
> looks similar to ld.bfd's -static -pie generation, even without the -static
> part.

[hjl@gnu-cfl-3 tmp]$ gcc -static-pie x.c 
[hjl@gnu-cfl-3 tmp]$ gcc -static-pie x.c -fuse-ld=lld
[hjl@gnu-cfl-3 tmp]$ gcc -static-pie x.c -fuse-ld=gold
/usr/local/bin/ld.gold: --no-dynamic-linker: unknown option
/usr/local/bin/ld.gold: use the --help option for usage information
collect2: error: ld returned 1 exit status
[hjl@gnu-cfl-3 tmp]$ 

> I assume this is because no other dynamic libraries are linked in when using
> -nostdlib and not specifying any dynamic library explicitly.
> 
> I do not know what the problem with glibc is, but static-pie kernels loaded
> by Limine with a non-0 load address (or shared objects with a non-0 load
> address for that matter) work perfectly fine if relocated (at or above
> whatever specified non-0 load address).

Does your kernel have any dynamic tags which need relocation?

[hjl@gnu-cfl-3 tmp]$ readelf -d /bin/ld

Dynamic section at offset 0x11f4a8 contains 35 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library:
[libbfd-2.42.50.0.1.20240523.so]
 0x0000000000000001 (NEEDED)             Shared library: [libctf.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libjansson.so.4]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000c (INIT)               0x6000
 0x000000000000000d (FINI)               0x4e594
 0x0000000000000019 (INIT_ARRAY)         0x1197f0
 0x000000000000001b (INIT_ARRAYSZ)       8 (bytes)
 0x000000000000001a (FINI_ARRAY)         0x1197f8
 0x000000000000001c (FINI_ARRAYSZ)       8 (bytes)
 0x000000006ffffef5 (GNU_HASH)           0x460
 0x0000000000000005 (STRTAB)             0x2148
 0x0000000000000006 (SYMTAB)             0x540
 0x000000000000000a (STRSZ)              4860 (bytes)
 0x000000000000000b (SYMENT)             24 (bytes)
 0x0000000070000000 (DT_X86_64_PLT)      0x7140
 0x0000000070000001 (DT_X86_64_PLTSZ)    0x10c0
 0x0000000070000003 (DT_X86_64_PLTENT)   0x10
 0x0000000000000015 (DEBUG)              0x0
 0x0000000000000003 (PLTGOT)             0x120728
 0x0000000000000002 (PLTRELSZ)           6432 (bytes)
 0x0000000000000014 (PLTREL)             RELA
 0x0000000000000017 (JMPREL)             0x39c8
 0x0000000000000007 (RELA)               0x37a0
 0x0000000000000008 (RELASZ)             552 (bytes)
 0x0000000000000009 (RELAENT)            24 (bytes)
 0x000000000000001e (FLAGS)              BIND_NOW
 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
 0x000000006ffffffe (VERNEED)            0x36a0
 0x000000006fffffff (VERNEEDNUM)         2
 0x000000006ffffff0 (VERSYM)             0x3444
 0x0000000000000024 (RELR)               0x52e8
 0x0000000000000023 (RELRSZ)             536 (bytes)
 0x0000000000000025 (RELRENT)            8 (bytes)
 0x0000000000000000 (NULL)               0x0
[hjl@gnu-cfl-3 tmp]$ 

These dynamic tags with addresses must be relocated before accessing the
memory.

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