Re: [PATCH v2 1/1] c++: ICE on on systems without mmap support [PR124806]

On 7/31/26 11:04, Torbjorn SVENSSON wrote:
> 
> 
> On 2026-07-31 05:31, Jason Merrill wrote:
>> On 7/29/26 8:03 AM, Torbjörn Svensson via Sourceware Forge wrote:
>>> From: Torbjörn SVENSSON <[email protected]>
>>>
>>> On systems without mmap support, cc1plus can crash when finishing module
>>> output after earlier errors prevented elf_out::begin from running.  In
>>> that case elf_out::end attempts to fill in the ELF header even though
>>> hdr.buffer was never initialized.
>>>
>>> gcc/cp/ChangeLog:
>>>
>>>     PR c++/124806
>>>     * module.cc (elf_out::begun): New data member.
>>
>> Let's call it "began" to match the one in module_processing_cookie.  I 
>> thought about trying to share that one flag, but I suppose it's 
>> probably necessary to distinguish between elf_out::begin and 
>> module_state::begin.
>>
>> OK with that tweak.
> 
> Renamed the member.
> 
> Pushed as r17-2849-g94556938452d2b.
> I'll push to releases/gcc-16 and releases/gcc-15 in a few days unless 
> someone objects.
> 

Note that gcc-16 is currently frozen.

Thanks,

Christophe


> Kind regards,
> Torbjörn
> 
>>
>>>     (elf_out::begin): Set it after successful initialization.
>>>     (elf_out::end): Do not finalize output that was never begun.
>>>
>>> Signed-off-by: Torbjörn SVENSSON <[email protected]>
>>> ---
>>>   gcc/cp/module.cc | 10 +++++++---
>>>   1 file changed, 7 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
>>> index f7569e688a26..156df4457463 100644
>>> --- a/gcc/cp/module.cc
>>> +++ b/gcc/cp/module.cc
>>> @@ -1511,6 +1511,7 @@ class elf_out : public elf, public 
>>> data::allocator {
>>>   private:
>>>     ptr_int_hash_map identtab;    /* Map of IDENTIFIERS to strtab 
>>> offsets. */
>>>     unsigned pos;            /* Write position in file.  */
>>> +  bool begun;            /* True if begin initialized output state.  */
>>>   #if MAPPED_WRITING
>>>     unsigned offset;        /* Offset of the mapping.  */
>>>     unsigned extent;        /* Length of mapping.  */
>>> @@ -1519,7 +1520,7 @@ private:
>>>   public:
>>>     elf_out (int fd, int e)
>>> -    :parent (fd, e), identtab (500), pos (0)
>>> +    :parent (fd, e), identtab (500), pos (0), begun (false)
>>>     {
>>>   #if MAPPED_WRITING
>>>       offset = extent = 0;
>>> @@ -2231,7 +2232,10 @@ elf_out::begin ()
>>>     memset (h, 0, sizeof (header));
>>>     hdr.pos = hdr.size;
>>>     write (hdr);
>>> -  return !get_error ();
>>> +  if (get_error ())
>>> +    return false;
>>> +  begun = true;
>>> +  return true;
>>>   }
>>>   /* Finish writing the file.  Write out the string & section tables.
>>> @@ -2240,7 +2244,7 @@ elf_out::begin ()
>>>   bool
>>>   elf_out::end ()
>>>   {
>>> -  if (fd >= 0)
>>> +  if (fd >= 0 && begun)
>>>       {
>>>         /* Write the string table.  */
>>>         unsigned strnam = name (".strtab");
>>
>