[PATCH] aarch64: Add support for %dtprel(var) and R_AARCH64_TLS_DTPREL64
Shivam Gupta
shivam98.tkg@gmail.com
Wed Mar 18 05:57:05 GMT 2026
Hello,
Apologise if I CCed wrong people for this patch to review.
I think Binutils side of this commit is prerequisite for llvm/lld side of
same work so PTAL.
Thanks,
Shivam
On Sat, Mar 14, 2026 at 2:12 AM Shivam Gupta <shivam98.tkg@gmail.com> wrote:
> This patch allows R_AARCH64_TLS_DTPREL64 relocations in non-allocated
> sections, which is required for DWARF debug information when using
> Thread Local Storage. This matches the behavior in LLD.
>
> Also a new syntax to parse dtprel operator use to describe tls
> location in debug information. Please see the reference 3 below.
>
> References:
> - https://github.com/llvm/llvm-project/pull/146572
> [AArch64] Support TLS variables in debug info
> - https://github.com/llvm/llvm-project/pull/183962
> [LLD][AArch64] Handle R_AARCH64_TLS_DTPREL64 in non-alloc sections
> - https://github.com/ARM-software/abi-aa/pull/330
> [AAELF64] Allow R_AARCH64_TLS_DTPREL to be used statically.
>
> bfd/
> * elfnn-aarch64.c (elfNN_aarch64_final_link_relocate): Handle
> BFD_RELOC_AARCH64_TLS_DTPREL.
>
> gas/
> * config/tc-aarch64.c (s_aarch64_cons): Parse %dtprel(var) syntax.
> * testsuite/gas/aarch64/tls-debug.s: New test.
> * testsuite/gas/aarch64/tls-debug.d: Run the test.
>
> gold/
> * aarch64-reloc-property.h (code_to_array_index): Handle
> R_AARCH64_TLS_DTPREL64.
> * aarch64.cc (Relocate::relocate): Handle R_AARCH64_TLS_DTPREL64.
>
> ld/
> * testsuite/ld-aarch64/tls-debug.s: New test.
> * testsuite/ld-aarch64/tls-debug.d: Run the test.
>
> Signed-off-by: Shivam Gupta <shivam98.tkg@gmail.com>
> ---
> bfd/elfnn-aarch64.c | 12 +++++++
> gas/config/tc-aarch64.c | 44 +++++++++++++++++++++++++
> gas/testsuite/gas/aarch64/tls-debug.d | 10 ++++++
> gas/testsuite/gas/aarch64/tls-debug.s | 9 +++++
> gold/aarch64-reloc-property.h | 2 ++
> gold/aarch64.cc | 8 ++++-
> ld/testsuite/ld-aarch64/aarch64-elf.exp | 1 +
> ld/testsuite/ld-aarch64/tls-debug.d | 9 +++++
> ld/testsuite/ld-aarch64/tls-debug.s | 9 +++++
> 9 files changed, 103 insertions(+), 1 deletion(-)
> create mode 100644 gas/testsuite/gas/aarch64/tls-debug.d
> create mode 100644 gas/testsuite/gas/aarch64/tls-debug.s
> create mode 100644 ld/testsuite/ld-aarch64/tls-debug.d
> create mode 100644 ld/testsuite/ld-aarch64/tls-debug.s
>
> diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
> index 66049c81..acf207dd 100644
> --- a/bfd/elfnn-aarch64.c
> +++ b/bfd/elfnn-aarch64.c
> @@ -6496,6 +6496,18 @@ elfNN_aarch64_final_link_relocate (reloc_howto_type
> *howto,
> *unresolved_reloc_p = false;
> break;
>
> + case BFD_RELOC_AARCH64_TLS_DTPREL:
> + /* Handle R_AARCH64_TLS_DTPREL64 in non-alloc sections */
> + if (!(input_section->flags & SEC_ALLOC))
> + {
> + value -= dtpoff_base (info);
> + value += rel->r_addend;
> +
> + bfd_put_64 (output_bfd, value, contents + rel->r_offset);
> + }
> + *unresolved_reloc_p = false;
> + break;
> +
> case BFD_RELOC_AARCH64_TLSDESC_OFF_G0_NC:
> case BFD_RELOC_AARCH64_TLSDESC_OFF_G1:
> if (globals->root.sgot == NULL)
> diff --git a/gas/config/tc-aarch64.c b/gas/config/tc-aarch64.c
> index cd761634..6cc7481a 100644
> --- a/gas/config/tc-aarch64.c
> +++ b/gas/config/tc-aarch64.c
> @@ -2229,6 +2229,40 @@ s_aarch64_cons (int nbytes)
> {
> struct reloc_table_entry *reloc;
>
> + /* Check for %dtprel(var) syntax */
> + if (*input_line_pointer == '%')
> + {
> + char *p = ++input_line_pointer; /* skip '%' */
> +
> + /* Look for "dtprel" */
> + if (strncmp (p, "dtprel", 6) == 0 && p[6] == '(')
> + {
> + input_line_pointer = p + 7; /* Skip "dtprel(" */
> +
> + /* Parse the symbol inside the parentheses */
> + expression (&exp);
> +
> + /* Ensure we have a closing parenthesis */
> + if (*input_line_pointer == ')')
> + input_line_pointer++;
> + else
> + as_bad (_("missing ')' after %%dtprel(...)"));
> +
> + /* Create the fixup using your DTPREL ID */
> + addressT where = frag_now_fix ();
> + fix_new_exp (frag_now, where, nbytes, &exp, 0,
> + BFD_RELOC_AARCH64_TLS_DTPREL);
> +
> + char *dest = frag_more (nbytes);
> + memset (dest, 0, nbytes);
> + continue;
> + }
> + else
> + {
> + as_bad (_("unknown relocation operator %%%s"), p);
> + }
> + }
> +
> expression (&exp);
>
> if (exp.X_op != O_symbol)
> @@ -3292,6 +3326,15 @@ static struct reloc_table_entry reloc_table[] =
> 0,
> 0},
>
> + /* TLS relative offset. */
> + {"dtprel", 0,
> + 0, /* adr_type */
> + 0,
> + 0,
> + 0,
> + 0,
> + BFD_RELOC_AARCH64_TLS_DTPREL},
> +
> /* Lower 16 bit offset into GOT entry for a symbol */
> {"tlsdesc_off_g0_nc", 0,
> 0, /* adr_type */
> @@ -10114,6 +10157,7 @@ md_apply_fix (fixS * fixP, valueT * valP, segT seg)
> case BFD_RELOC_AARCH64_TLSLE_MOVW_TPREL_G1:
> case BFD_RELOC_AARCH64_TLSLE_MOVW_TPREL_G1_NC:
> case BFD_RELOC_AARCH64_TLSLE_MOVW_TPREL_G2:
> + case BFD_RELOC_AARCH64_TLS_DTPREL:
> S_SET_THREAD_LOCAL (fixP->fx_addsy);
> /* Should always be exported to object file, see
> aarch64_force_relocation(). */
> diff --git a/gas/testsuite/gas/aarch64/tls-debug.d
> b/gas/testsuite/gas/aarch64/tls-debug.d
> new file mode 100644
> index 00000000..a64ff67f
> --- /dev/null
> +++ b/gas/testsuite/gas/aarch64/tls-debug.d
> @@ -0,0 +1,10 @@
> +#as:
> +#objdump: -r
> +#target: aarch64*-*-*
> +
> +#...
> +RELOCATION RECORDS FOR \[\.debug_info\]:
> +OFFSET +TYPE +VALUE
> +0+0 R_AARCH64_TLS_DTPREL64 +var
> +0+8 R_AARCH64_TLS_DTPREL64 +var\+0x0+1
> +#...
> diff --git a/gas/testsuite/gas/aarch64/tls-debug.s
> b/gas/testsuite/gas/aarch64/tls-debug.s
> new file mode 100644
> index 00000000..9590ad40
> --- /dev/null
> +++ b/gas/testsuite/gas/aarch64/tls-debug.s
> @@ -0,0 +1,9 @@
> +.section .tdata,"awT",@progbits
> +.skip 8 // Force var to have an offset of 8
> +.globl var
> +var:
> + .word 0
> +
> +.section .debug_info,"",@progbits
> + .xword %dtprel(var)
> + .xword %dtprel(var+1)
> diff --git a/gold/aarch64-reloc-property.h b/gold/aarch64-reloc-property.h
> index 986adf9d..c1ce0033 100644
> --- a/gold/aarch64-reloc-property.h
> +++ b/gold/aarch64-reloc-property.h
> @@ -220,6 +220,8 @@ class AArch64_reloc_property_table
> code_to_array_index(unsigned int code) const
> {
> if (code == 0) return 0;
> + if (code == elfcpp::R_AARCH64_TLS_DTPREL64)
> + return 0;
> if (!((code >= elfcpp::R_AARCH64_ABS64 &&
> code <= elfcpp::R_AARCH64_LD64_GOTPAGE_LO15)
> || (code >= elfcpp::R_AARCH64_TLSGD_ADR_PREL21 &&
> diff --git a/gold/aarch64.cc b/gold/aarch64.cc
> index 9ef5df79..5575f78b 100644
> --- a/gold/aarch64.cc
> +++ b/gold/aarch64.cc
> @@ -7330,13 +7330,19 @@ Target_aarch64<size,
> big_endian>::Relocate::relocate(
> gsym, psymval, view, address);
> break;
>
> + case elfcpp::R_AARCH64_TLS_DTPREL64:
> + {
> + uint64_t val = psymval->value (object, 0) + rela.get_r_addend ();
> + elfcpp::Swap<64, big_endian>::writeval (view, val);
> + break;
> + }
> +
> // These are dynamic relocations, which are unexpected when linking.
> case elfcpp::R_AARCH64_COPY:
> case elfcpp::R_AARCH64_GLOB_DAT:
> case elfcpp::R_AARCH64_JUMP_SLOT:
> case elfcpp::R_AARCH64_RELATIVE:
> case elfcpp::R_AARCH64_IRELATIVE:
> - case elfcpp::R_AARCH64_TLS_DTPREL64:
> case elfcpp::R_AARCH64_TLS_DTPMOD64:
> case elfcpp::R_AARCH64_TLS_TPREL64:
> case elfcpp::R_AARCH64_TLSDESC:
> diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp
> b/ld/testsuite/ld-aarch64/aarch64-elf.exp
> index a0a8867d..096f5f9f 100644
> --- a/ld/testsuite/ld-aarch64/aarch64-elf.exp
> +++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp
> @@ -252,6 +252,7 @@ run_dump_test "tls-relax-ld-le-small-ilp32"
> run_dump_test "tls-relax-ld-le-tiny"
> run_dump_test "tls-relax-ld-le-tiny-ilp32"
> run_dump_test "tls-desc-ie"
> +run_dump_test "tls-debug"
> run_dump_test "tls-desc-ie-ilp32"
> run_dump_test "tls-relax-gdesc-le-2"
> run_dump_test "tls-relax-gdesc-le-2-ilp32"
> diff --git a/ld/testsuite/ld-aarch64/tls-debug.d
> b/ld/testsuite/ld-aarch64/tls-debug.d
> new file mode 100644
> index 00000000..4344b02e
> --- /dev/null
> +++ b/ld/testsuite/ld-aarch64/tls-debug.d
> @@ -0,0 +1,9 @@
> +#source: tls-debug.s
> +#ld: -shared -T relocs.ld -e0
> +#objdump: -s -j .debug_info
> +
> +#...
> +Contents of section .debug_info:
> +#...
> + [0-9a-f]+ 08000000 00000000 09000000 00000000 .*
> +#...
> diff --git a/ld/testsuite/ld-aarch64/tls-debug.s
> b/ld/testsuite/ld-aarch64/tls-debug.s
> new file mode 100644
> index 00000000..9590ad40
> --- /dev/null
> +++ b/ld/testsuite/ld-aarch64/tls-debug.s
> @@ -0,0 +1,9 @@
> +.section .tdata,"awT",@progbits
> +.skip 8 // Force var to have an offset of 8
> +.globl var
> +var:
> + .word 0
> +
> +.section .debug_info,"",@progbits
> + .xword %dtprel(var)
> + .xword %dtprel(var+1)
> --
> 2.34.1
>
>
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