[PATCH 05/12] include: libsframe: define new flag SFRAME_F_FDE_FUNC_START_ADDR_PCREL

[Jens Remus]

On 28.05.2025 07:40, Indu Bhagat via Binutils wrote:
> Add a new flag SFRAME_F_FDE_FUNC_START_ADDR_PCREL to SFrame stack trace
> format.  If set, this flag indicates that the function start address
> field (sfde_func_start_address) is the offset to the function start
> address from the SFrame FDE function start address field itself.
> 
> Such an encoding is friendlier to the exisitng PC-REL relocations
> available in the ABIs supported in SFrame: AMD64 (R_X86_64_PC32) and
> AArch64 (R_AARCH64_PREL32).  In subsequent patches, we will make the
> implementation in gas and ld to both:
>   - emit the values in the same (above-mentioned) encoding uniformly.
>   - set the flag SFRAME_F_FDE_FUNC_START_ADDR_PCREL in the SFrame header
>     for consumers to be able to distinguish.

> diff --git a/include/sframe.h b/include/sframe.h

> @@ -82,9 +82,15 @@ extern "C"
>  /* Various flags for SFrame.  */
>  
>  /* Function Descriptor Entries are sorted on PC.  */
> -#define SFRAME_F_FDE_SORTED	0x1
> +#define SFRAME_F_FDE_SORTED		    0x1
>  /* Functions preserve frame pointer.  */
> -#define SFRAME_F_FRAME_POINTER 0x2
> +#define SFRAME_F_FRAME_POINTER		    (0x1 << 1)
> +/* Function start address in SFrame FDE is encoded as the distance from the
> +   location of the sfde_func_start_address to the start PC of the function.
> +   If absent, the function start address in SFrame FDE is encoded as the
> +   distance from the start of the SFrame FDE section to the start PC of the
> +   function.  */
> +#define SFRAME_F_FDE_FUNC_START_ADDR_PCREL  (0x1 << 2)

1.......10........20........30........40........50........60........70..
I would prefer to use hexadecimal values for the flags (and perhaps use
two digits, as the flags field is uint8_t):

#define SFRAME_F_FDE_SORTED			0x01
#define SFRAME_F_FRAME_POINTER			0x02
#define SFRAME_F_FDE_FUNC_START_ADDR_PCREL	0x04

This would also match with how you document them in your subsequent patch
(which I would merge into this one).

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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