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

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.

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");
>