RFR: 8374744: Enable dumping of APX EGPRs (R16–R31) in JVM fatal error logs

[Sandhya Viswanathan]

On Wed, 7 Jan 2026 20:28:14 GMT, Srinivas Vamsi Parasa <sparasa at openjdk.org> wrote:

> The goal of this PR is to add support for printing the values of APX extended general-purpose registers (EGPRs, R16-R31) in hs_err_pid* crash logs on x86 platforms with APX support. The implementation detects APX support at runtime and attempts to dump the additional registers when available, improving post-mortem debugging capabilities.

src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp line 449:

> 447:   // Dump APX EGPRs (R16-R31)
> 448:   apx_state* apx = get_apx_state(uc);
> 449:   if (UseAPX && apx != nullptr) {

This could be done as:
apx_state* apx = UseAPX ? get_apx_state(uc) : nullptr;
if (apx != nullptr) {

src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp line 469:

> 467:     st->print(", R30=" INTPTR_FORMAT, (intptr_t)apx->regs[14]);
> 468:     st->print(", R31=" INTPTR_FORMAT, (intptr_t)apx->regs[15]);
> 469:     st->cr();

This could be done with a for loop.

src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp line 556:

> 554:         CASE_PRINT_REG_APX(30, "R30=", 14); break;
> 555:         CASE_PRINT_REG_APX(31, "R31=", 15); break;
> 556:       }

Don't need a switch case here. Could be achieved with something like below:

st->print("R%d=", n);
print_location(st, apx->regs[n]);

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PR Review Comment: https://git.openjdk.org/jdk/pull/29098#discussion_r2700175735
PR Review Comment: https://git.openjdk.org/jdk/pull/29098#discussion_r2733973731
PR Review Comment: https://git.openjdk.org/jdk/pull/29098#discussion_r2733989504