[crac] RFR: 8368929: [CRaC] Move CPUFeatures check to C/R engine

[Jan Kratochvil]

On Tue, 30 Sep 2025 13:17:54 GMT, Radim Vansa <rvansa at openjdk.org> wrote:

> Right now the logic checking if CPU features used before checkpoint match current CPU features is in VM code. VM stores and retrieves CPU features through C/R API's user_data extension. This is convenient when we have a single image that can be either accepted or rejected, but does not offer the flexibility for C/R engine to select the best image for current execution environment.
> 
> The goal of this issue is to move to a declarative API that will express the requirements using more abstract means, labels (for CPU architecture) and bitmaps (for CPU features).

src/hotspot/share/include/crlib/crlib.h line 85:

> 83: #define RESTORE_ERROR_INVALID   -4 // image is not suitable (e.g. corruption or wrong architecture)
> 84: #define RESTORE_ERROR_MEMORY    -5 // memory allocation failure during restore
> 85: #define RESTORE_ERROR_PROCINFO  -6 // the process cannot fetch information about itself

Cannot it be an enum?

src/hotspot/share/runtime/crac.cpp line 527:

> 525:   // Since the check itself is delegated to the C/R Engine we will simply
> 526:   // skip the check here (or prevent storing the features in the image).
> 527: #ifdef __x86_64__

One should not use `#ifdef` as it may lead to compilation errors on other arches.

src/hotspot/share/runtime/crac.cpp line 589:

> 587:   if (ret == RESTORE_ERROR_INVALID) {
> 588:     log_error(crac)("CRaC engine failed to restore from %s: the image is either corrupted or does not match current CPU", CRaCRestoreFrom);
> 589: #ifdef __x86_64__

Likewise one should not use `#ifdef` as it may lead to compilation errors on other arches.

src/java.base/share/native/libcrexec/image_constraints.cpp line 39:

> 37: 
> 38: static FILE *open_tags(const char *image_location, const char *mode) {
> 39:    char fname[PATH_MAX];

whitespace

src/java.base/share/native/libcrexec/image_constraints.cpp line 61:

> 59:         fprintf(f, LABEL_PREFIX "%s=%s\n", tag.name, static_cast<const char *>(tag.data));
> 60:     } else {
> 61:         fprintf(f, BITMAP_PREFIX "%s=", tag.name);

indentation 2 vs. 4

src/java.base/share/native/libcrexec/image_constraints.cpp line 77:

> 75: 
> 76: static inline unsigned char from_hex(char c, bool *err) {
> 77:     if (c >= '0' && c <= '9') {

again changed indentation, more occurences in this file

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PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2393876679
PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2393871031
PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2393871594
PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2393878601
PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2393881789
PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2393884186