Re: [PATCH v5 26/26] xen/riscv: do a 4th linking pass if necessary

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.07.2026 10:19, Oleksii Kurochko wrote:
> On 7/6/26 6:13 PM, Jan Beulich wrote:
>> On 06.07.2026 17:58, Oleksii Kurochko wrote:
>>> Embedding the symbol table can shift sections and flip relaxation
>>> decisions, changing code size and thus the set of emitted symbols
>>> (e.g. gap end markers).
>>
>> What difference in symbols is there? (And: Do you mean the ELF symbol
>> table or what tools/symbols emits?) On ...
> 
> The ELF symbol tables of .xen-syms.0 and .xen-syms.1 are identical
> (same names, types, and count; only addresses past a certain point
> differ). The difference is in what tools/symbols emits: the
> address-only "end of symbol" entry produced when want_symbol_end()
> is true, i.e. when a sized text symbol's end doesn't reach the next
> symbol's address:
> 
>      static bool want_symbol_end(unsigned int idx)
>      {
>          return table[idx].size &&
>                 (idx + 1 == table_cnt ||
>                  table[idx].addr + table[idx].size < table[idx + 1].addr);
>      }
> 
> In pass 1 (generated from .xen-syms.0): simple_strtoull is at
> 0xffffffffc00c0444 with size 0x16c, ending at 0xffffffffc00c05b0,
> while turn_on_mmu (alignment-pinned) starts at 0xffffffffc00c05c0.
> 16-byte gap -> the end marker at ...c05b0 is emitted.
> 
> In pass 2 (generated from .xen-syms.1): simple_strtoull moved to
> 0xffffffffc00c0454 (same size), ending at exactly 0xffffffffc00c05c0
> == turn_on_mmu. No gap -> no end marker. Hence symbols_addresses
> shrinks by 8 and symbols_names by 1 (the marker's empty name).
> 
>>
>>>   Re-link with a regenerated table when its
>>> size differs from the previous pass.
>>>
>>> This mirrors commit 35de7285d508 ("Arm: do a 4th linking pass if
>>> necessary"), which riscv didn't receive when the underlying
>>> pass-2-vs-pass-3 check was extended to it in commit aa786d6e3467
>>> ("non-x86/symbols: check table sizes don't change between linking
>>> passes 2 and 3").
>>
>> ... Arm the problem was with a symbol (dis)appearing from/in the ELF
>> symbol table. The situation looks to be different here. Sadly ...
> 
> I will rephrase then this paragraph to:
> 
> This takes the same remedy as commit 35de7285d508 ("Arm: do a 4th
> linking pass if necessary"), though the underlying cause differs:
> here no symbol (dis)appears from the ELF symbol table; instead the
> set of end markers emitted by tools/symbols legitimately changes,
> because want_symbol_end() depends on code layout, and layout differs
> between passes due to linker relaxation.
> 
> Or it could be just dropped.

Please don't drop it.

Jan