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From: "jskumari at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/100799] Stackoverflow in optimized code on PPC
Date: Mon, 17 Oct 2022 09:42:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100799

--- Comment #18 from Surya Kumari Jangala <jskumari at gcc dot gnu.org> ---
I git cloned and built flexiblas to see what is the frame size and what is =
the
assembly code generated for the flexiblas C wrapper routine for dgebal.

The important assembly code snippets for dgebal.c :

// r23-r31 are saved in the callee frame
   std     r23,-72(r1)
   std     r24,-64(r1)
   ...
   ...
   std     r31,-8(r1)

// allocate the stack frame
   stdu    r1,-112(r1)

// save the parameter registers r3-r10 into r23-r30
   mr      r30,r3
   ...
   mr      r23,r10

// some of the param regs are used as temps
   ld      r3,0(r31)
   lwz     r11,16(r3)

// populate the param registers appropriately
   mr      r3,r30
   ...
   mr      r10,r23

// make the call to the fortran dgebal routine
   bctrl

// restore r1
   addi    r1,r1,112

// restore r23-r31
   ld      r23,-72(r1)
   ...
   ld      r31,-8(r1)

// return
   blr

As we can see, the frame size allocated is only 112 out of which 32 is for
things like LR, TOC etc. and 72 is needed to save r23-r31. So clearly, the
wrapper routine is not allocating any parameter save area in it's frame.
Now, the dgebal fortran routine writes into the caller's frame thereby
corrupting a callee save register (one of r23-r31). So when control returns
back from the wrapper routine to the fortran routine dgeev, we see a corrup=
ted
value.=