[PULL 09/26] linux-user/hppa: Document non-use of setup_sigtramp

[Laurent Vivier <laurent@vivier.eu>]

From: Richard Henderson <richard.henderson@linaro.org>

We cannot use a raw sigtramp page for hppa,
but must wait for full vdso support.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210929130553.121567-10-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/hppa/target_signal.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/linux-user/hppa/target_signal.h b/linux-user/hppa/target_signal.h
index 7f525362e91a..d558119ee7bd 100644
--- a/linux-user/hppa/target_signal.h
+++ b/linux-user/hppa/target_signal.h
@@ -71,4 +71,18 @@ typedef struct target_sigaltstack {
 /* mask for all SS_xxx flags */
 #define TARGET_SS_FLAG_BITS  TARGET_SS_AUTODISARM
 
+/*
+ * We cannot use a bare sigtramp page for hppa-linux.
+ *
+ * Unlike other guests where we use the instructions at PC to validate
+ * an offset from SP, the hppa libgcc signal frame fallback unwinding uses
+ * the PC address itself to find the frame.  This is due to the fact that
+ * the hppa grows the stack upward, and the frame is of unknown size.
+ *
+ * TODO: We should be able to use a VDSO to address this, by providing
+ * proper unwind info for the sigtramp code, at which point the fallback
+ * unwinder will not be used.
+ */
+#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 0
+
 #endif /* HPPA_TARGET_SIGNAL_H */
-- 
2.31.1