8346193: Test runtime/ErrorHandling/TestDwarf.java fails build with clang17

[sendaoYan]

Hi all,
Function frame::oops_do_internal in src/hotspot/share/runtime/frame.cpp assign value to a nullptr char *t and intended to cause jvm crash. But after the assignment the nullptr do not use anymore, so clang17 consider the char *t initialization and assignment is "dead code". This PR add volatile modifier to char *t, to make avoid clang do the "dead code" elimination. Risk is low.

Here is the example explain the "dead code" elimination.

1. Without volatile modifier, clang will delete the "dead code" and cause no more Segmentation fault error by -O1.

> cat demo.c 
int main() { char *t = 0; *t = 'c'; return 0; }
> clang -O0 demo.c && ./a.out ; echo $?
Segmentation fault (core dumped)
139
> clang -O1 demo.c && ./a.out ; echo $?
0

2. With volatile modifier, clang do not delete the "dead code" again and and the expected Segmentation fault occur by -O1.

> cat demo.c 
int main() { volatile char *t = 0; *t = 'c'; return 0; }
> clang -O0 demo.c && ./a.out ; echo $?
Segmentation fault (core dumped)
139
> clang -O1 demo.c && ./a.out ; echo $?
Segmentation fault (core dumped)
139

---

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Issue

• JDK-8346193: Test runtime/ErrorHandling/TestDwarf.java fails build with clang17 (Bug - P4)

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[mlbridge]

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• 00: Full (3a8e4349)

[dholmes-ora]

Suggested change

	volatile char *t = nullptr; // Use volatile modifier to make clang avoid 'dead code' elimination
	volatile char* t = nullptr; // Use volatile to prevent compiler from optimising away the store