feat(setjmp): x86_64 setjmp/longjmp/sigsetjmp

2026-09-03 17:39:20 -04:00
parent dec1017527
commit b2d588885e
6 changed files with 684 additions and 0 deletions
@@ -0,0 +1,117 @@
+#ifndef VLIBC_SETJMP_H
+#define VLIBC_SETJMP_H
+
+/*
+ * vlibc — <setjmp.h>.
+ *
+ * Non-local jumps. setjmp(env) saves the calling environment and returns 0;
+ * longjmp(env, val) makes that setjmp return val, with 0 coerced to 1 so the
+ * two returns are distinguishable. sigsetjmp/siglongjmp additionally save and
+ * restore the signal mask when the buffer's saved-mask flag is set.
+ *
+ * jmp_buf is an array type (C23 7.13.1 requires it); both types below are
+ * arrays of unsigned long. The word layout is ABI: the x86_64 assembly in
+ * src/setjmp/x86_64/{setjmp,longjmp,sigsetjmp,siglongjmp}.s reads and writes
+ * exactly these slots. This comment is the single authoritative map — keep it
+ * and those files in sync:
+ *
+ *   [0] rbx             callee-saved general registers (System V AMD64 ABI)
+ *   [1] rbp
+ *   [2] r12
+ *   [3] r13
+ *   [4] r14
+ *   [5] r15
+ *   [6] rsp             the caller's stack pointer (just past the return address)
+ *   [7] rip             the return address, where longjmp resumes execution
+ *   [8] mxcsr           SSE control/status register (stmxcsr/ldmxcsr)
+ *   [9] x87 cw          x87 control word (fnstcw/fldcw)
+ *
+ * sigjmp_buf extends the base layout with two more words:
+ *
+ *   [10] saved-mask flag (1 when the signal mask was saved)
+ *   [11] signal mask     (the x86_64 Linux sigset_t: a single 64-bit word)
+ *
+ * Because the base layout occupies words 0..9 of both types, the plain
+ * setjmp/longjmp assembly works verbatim on sigjmp_buf storage as well.
+ */
+
+#include <vlibc/features.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Word counts and per-slot indices (see the authoritative map above). */
+#define VLIBC_JMP_BUF_WORDS 10
+#define VLIBC_JMP_RBX 0
+#define VLIBC_JMP_RBP 1
+#define VLIBC_JMP_R12 2
+#define VLIBC_JMP_R13 3
+#define VLIBC_JMP_R14 4
+#define VLIBC_JMP_R15 5
+#define VLIBC_JMP_RSP 6
+#define VLIBC_JMP_RIP 7
+#define VLIBC_JMP_MXCSR 8
+#define VLIBC_JMP_X87CW 9
+
+#define VLIBC_SIGJMP_BUF_WORDS 12
+#define VLIBC_SIGJMP_FLAG 10
+#define VLIBC_SIGJMP_MASK 11
+
+typedef unsigned long jmp_buf[VLIBC_JMP_BUF_WORDS];
+typedef unsigned long sigjmp_buf[VLIBC_SIGJMP_BUF_WORDS];
+
+/*
+ * Save the calling environment and return 0; after longjmp(env, val) the
+ * matching setjmp invocation returns val. A macro (C23 7.13.1: usable without
+ * a prototype in scope); it expands to _setjmp(env).
+ */
+#define setjmp(env) _setjmp(env)
+
+/*
+ * Like setjmp, plus the current signal mask is saved into env when savemask is
+ * nonzero (siglongjmp then restores it). Macro expanding to
+ * __sigsetjmp(env, savemask).
+ */
+#define sigsetjmp(env, savemask) __sigsetjmp(env, savemask)
+
+/*
+ * The save behind the setjmp macro; identical semantics (POSIX _setjmp).
+ */
+int
+_setjmp(jmp_buf env); // NOLINT(bugprone-reserved-identifier)
+
+/*
+ * Restore the environment saved by _setjmp/setjmp and make it return val, with
+ * 0 coerced to 1. Does not return.
+ */
+__attribute__((noreturn)) void
+_longjmp(jmp_buf env, int val); // NOLINT(bugprone-reserved-identifier)
+
+/*
+ * ISO C longjmp: same as _longjmp.
+ */
+__attribute__((noreturn)) void
+longjmp(jmp_buf env, int val);
+
+/*
+ * The save behind the sigsetjmp macro. Implementation-reserved name, so the
+ * public API keeps only the macro; declared because the macro expansion must
+ * have a prototype in scope (C23 removed implicit declarations).
+ */
+int
+__sigsetjmp(sigjmp_buf env, int savemask); // NOLINT(bugprone-reserved-identifier)
+
+/*
+ * Restore the environment saved by sigsetjmp and make it return val, with 0
+ * coerced to 1; when the buffer's saved-mask flag is set, the signal mask is
+ * restored first. Does not return.
+ */
+__attribute__((noreturn)) void
+siglongjmp(sigjmp_buf env, int val);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* VLIBC_SETJMP_H */