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

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.

> 	(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");