Re: [PATCH] gdb: LoongArch: Add internal TLS support

[Simon Marchi <simark@simark.ca>]

On 7/13/26 6:37 AM, Hui Li wrote:
> Implements the LoongArch-specific get_tls_dtv_addr() and uses
> svr4_tls_register_tls_methods() to register it, together with
> svr4_tls_get_thread_local_address as the get_thread_local_address
> gdbarch method, to support internal TLS address lookup.
> 
> LoongArch doesn't need get_tls_dtp_offset since musl's DTP_OFFSET
> is defined as 0.
> 
> This is the LoongArch version of commit c34309bea22
> ("Internal TLS support for aarch64, x86_64, riscv, ppc64, and s390x").
> 
> Depends-On: bfc3ac0d13b
> ("LoongArch: Support R_LARCH_TLS_DTPREL32/64 used in debug section")
> 
> Before:
> 
> make check-gdb TESTS="gdb.base/tls-nothreads.exp"
> === gdb Summary ===
> 
>   # of expected passes		101
>   # of known failures		48
> 
> make check-gdb TESTS="gdb.base/tls-dlobj.exp"
> === gdb Summary ===
> 
>   # of expected passes		261
> 
> After:
> 
> make check-gdb TESTS="gdb.base/tls-nothreads.exp"
> === gdb Summary ===
> 
>   # of expected passes		302
> 
> make check-gdb TESTS="gdb.base/tls-dlobj.exp"
> === gdb Summary ===
> 
>   # of expected passes		523
> 
> Signed-off-by: Hui Li <lihui@loongson.cn>

Great, thanks.  I compared the implementation to Aarch64, and it's very
similar, so it looks reasonable to me.

One nit below:

> @@ -1137,6 +1138,57 @@ init_loongarch_linux_record_tdep (struct gdbarch *gdbarch)
>    loongarch_linux_record_tdep.arg7 = LOONGARCH_A0_REGNUM + 6;
>  }
>  
> +/* Fetch and return the TLS DTV (dynamic thread vector) address for PTID.
> +   Throw a suitable TLS error if something goes wrong.  */
> +
> +static CORE_ADDR
> +loongarch_linux_get_tls_dtv_addr (struct gdbarch *gdbarch, ptid_t ptid,
> +				  svr4_tls_libc libc)
> +{
> +  /* On LoongArch, the thread pointer is found in TP.  */
> +  regcache *regcache
> +    = get_thread_arch_regcache (current_inferior (), ptid, gdbarch);
> +  target_fetch_registers (regcache, LOONGARCH_TP_REGNUM);
> +  ULONGEST thr_ptr;
> +  if (regcache->cooked_read (LOONGARCH_TP_REGNUM, &thr_ptr) != REG_VALID)
> +    throw_error (TLS_GENERIC_ERROR, _("Unable to fetch thread pointer"));
> +
> +  CORE_ADDR dtv_ptr_addr;
> +  switch (libc)
> +    {
> +      case svr4_tls_libc_musl:
> +	/* MUSL: The DTV pointer is found at the very end of the pthread
> +	   struct which is located *before* the thread pointer.  I.e.
> +	   the thread pointer will be just beyond the end of the struct,
> +	   so the address of the DTV pointer is found one pointer-size
> +	   before the thread pointer.  */
> +	dtv_ptr_addr = thr_ptr - (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);
> +	break;
> +      case svr4_tls_libc_glibc:
> +	/* GLIBC:  The thread pointer (TP) points just beyond the end of
> +	   the TCB (thread control block).  On LoongArch, this struct
> +	   (tcbhead_t) is defined to contain two pointers.  The first is
> +	   a pointer to the DTV and the second is a pointer to private
> +	   data.  So the DTV pointer address is found two pointer-size
> +	   before thread pointer.  */
> +
> +	dtv_ptr_addr = thr_ptr - 2 * (gdbarch_ptr_bit (gdbarch) / TARGET_CHAR_BIT);

Remove empty line above.

With, this:

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon