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Ports/gdb: Implement wait and mourn_inferior overrides for our target

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While troubleshooting why gdb wasn't working when attempting to debug
serenity programs I noticed two things:

 - The contract of serenity's `waitpid(..)` appears to be slightly
   different than the generic ptrace target expects. We need to make
   sure we pass `WSTOPPED`, and it can return different errno values
   that we would want to re-try on.

-  The contract of serenity's `ptrace(..)` implementation appears to
   diverge as well, as we are expected to call `PT_ATTACH` before we
   call `PT_CONTINUE`, otherwise `ptrace(..)` will just error out.

These two patches fix the behavior of wait and mourn_inferior so that
they work as expected on serenity and allow us to attach and then wait
for a process to exit while running under gdb.
This commit is contained in:
Brian Gianforcaro 2022-02-20 00:46:03 -08:00 • committed by Andreas Kling
parent f01e1d0c17
commit e56262caed
Notes: sideshowbarker 2024-07-17 18:29:47 +09:00
7 changed files with 195 additions and 4 deletions
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2
Ports/gdb/patches/0001-gdb-Disable-xmalloc-for-alternate_signal_stack-for-s.patch
View file

@ -1,7 +1,7 @@
From 32bfc7a161e6bf10decbf29b31c7b547cf250d3a Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <b.gianfo@gmail.com>
Date: Sat, 19 Feb 2022 19:46:06 -0800
Subject: [PATCH 1/4] gdb: Disable xmalloc for alternate_signal_stack for
Subject: [PATCH 1/6] gdb: Disable xmalloc for alternate_signal_stack for
serenity
---

2
Ports/gdb/patches/0002-serenity-Add-basic-ptrace-based-native-target-for-Se.patch
View file

@ -1,7 +1,7 @@
From 883a25f5ed8fd8f13b8e30aed3a25001839d892c Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <b.gianfo@gmail.com>
Date: Tue, 28 Dec 2021 04:35:47 -0800
Subject: [PATCH 2/4] serenity: Add basic ptrace based native target for
Subject: [PATCH 2/6] serenity: Add basic ptrace based native target for
SerenityOS/i386
---

2
Ports/gdb/patches/0003-gdb-Add-build-support-for-SerenityOS.patch
View file

@ -1,7 +1,7 @@
From e87fd74df2c7fcb4b146eb09b5b710a45003999a Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <b.gianfo@gmail.com>
Date: Sat, 19 Feb 2022 19:47:42 -0800
Subject: [PATCH 3/4] gdb: Add build support for SerenityOS
Subject: [PATCH 3/6] gdb: Add build support for SerenityOS
---
bfd/config.bfd | 9 +++++++++

2
Ports/gdb/patches/0004-serenity-Fix-compiler-fpermissive-warnings-from-usin.patch
View file

@ -1,7 +1,7 @@
From 7a5e11d2e9cbe98af96faa4835592686bf261a23 Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <b.gianfo@gmail.com>
Date: Tue, 28 Dec 2021 04:39:25 -0800
Subject: [PATCH 4/4] serenity: Fix compiler -fpermissive warnings from using
Subject: [PATCH 4/6] serenity: Fix compiler -fpermissive warnings from using
latest GCC
---

114
Ports/gdb/patches/0005-serenity-Implement-custom-wait-override-for-the-sere.patch Normal file
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@ -0,0 +1,114 @@
From a80fc99e8f2e1c5ac1620a8c6c26d65daa98204e Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <b.gianfo@gmail.com>
Date: Sun, 20 Feb 2022 00:32:51 -0800
Subject: [PATCH 5/6] serenity: Implement custom wait override for the
serenity_nat_target
While troubleshooting why gdb wasn't working when attempting to debug
serenity programs I noticed two things:
- The contract of serenity's `waitpid(..)` appears to be slightly
different than the generic ptrace target expects. We need to make
sure we pass `WSTOPPED`, and it can return different errno values
that we would want to re-try on.
- The contract of serenity's `ptrace(..)` implementation appears to
diverge as well, as we are expected to call `PT_ATTACH` before we
call `PT_CONTINUE`, otherwise `ptrace(..)` will just error out.
Allow gdb to understand these differences, I've overloaded the
serenity_nat_target::wait(..) method and added the logic there.
---
gdb/serenity-nat.c | 62 +++++++++++++++++++++++++++++++++++++++++++++-
gdb/serenity-nat.h | 4 +++
2 files changed, 65 insertions(+), 1 deletion(-)
diff --git a/gdb/serenity-nat.c b/gdb/serenity-nat.c
index ff740d4..b1d39d4 100644
--- a/gdb/serenity-nat.c
+++ b/gdb/serenity-nat.c
@@ -10,4 +10,64 @@
#include "gdbsupport/gdb_wait.h"
#include "inf-child.h"
-#include "serenity-nat.h"
\ No newline at end of file
+#include "serenity-nat.h"
+
+ptid_t serenity_nat_target::wait (ptid_t ptid, struct target_waitstatus* ourstatus, target_wait_flags)
+{
+ int pid;
+ int status, save_errno;
+
+ do
+ {
+ set_sigint_trap ();
+
+ do
+ {
+ errno = 0;
+ pid = waitpid (ptid.pid (), &status, WSTOPPED);
+ if (errno != 0)
+ {
+ save_errno = errno;
+ perror_with_name (("waitpid"));
+ }
+ }
+ while (pid == -1 && (save_errno == EINTR || save_errno == EAGAIN));
+
+ clear_sigint_trap ();
+
+ if (pid == -1)
+ {
+ fprintf_unfiltered (gdb_stderr,
+ _("Child process unexpectedly missing: %s.\n"),
+ safe_strerror (save_errno));
+
+ /* Claim it exited with unknown signal. */
+ ourstatus->kind = TARGET_WAITKIND_SIGNALLED;
+ ourstatus->value.sig = GDB_SIGNAL_UNKNOWN;
+ return inferior_ptid;
+ }
+
+ /* Ignore terminated detached child processes. */
+ if (!WIFSTOPPED (status) && find_inferior_pid (this, pid) == nullptr)
+ pid = -1;
+ }
+ while (pid == -1);
+
+ store_waitstatus (ourstatus, status);
+
+ /* Serenity requires us to PT_ATTACH before we PT_CONTINUE, however GDB doesn't
+ * provide a hook for us to do that before we issue the PT_CONTINUE, so we are
+ * forced to do it here.
+ */
+ if (!m_attach_before_continue_called) {
+ errno = 0;
+ ptrace (PT_ATTACH, pid, (PTRACE_TYPE_ARG3)0, 0);
+ if (errno != 0) {
+ save_errno = errno;
+ printf_unfiltered (_("PT_ATTACH failed: %d - %s \n"), save_errno, safe_strerror (save_errno));
+ }
+ m_attach_before_continue_called = true;
+ }
+
+ return ptid_t (pid);
+}
diff --git a/gdb/serenity-nat.h b/gdb/serenity-nat.h
index dcd24ce..9ae3b87 100644
--- a/gdb/serenity-nat.h
+++ b/gdb/serenity-nat.h
@@ -11,6 +11,10 @@
class serenity_nat_target : public inf_ptrace_target
{
+ ptid_t wait (ptid_t, struct target_waitstatus *, target_wait_flags) override;
+
+private:
+ bool m_attach_before_continue_called { false };
};
#endif /* serenity-nat.h */
--
2.32.0

51
Ports/gdb/patches/0006-serenity-Implement-mourn_inferior-override-for-the-s.patch Normal file
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@ -0,0 +1,51 @@
From 1285f88fcd5a8eabf5536e5af8015777f2a64117 Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <b.gianfo@gmail.com>
Date: Sun, 20 Feb 2022 00:44:08 -0800
Subject: [PATCH 6/6] serenity: Implement mourn_inferior override for the
serenity_nat_target
We need to pass `WNOHANG` to our `waitpid(..)` call on SerenityOS,
otherwise we will wait forever.
---
gdb/serenity-nat.c | 14 ++++++++++++++
gdb/serenity-nat.h | 2 ++
2 files changed, 16 insertions(+)
diff --git a/gdb/serenity-nat.c b/gdb/serenity-nat.c
index b1d39d4..7789950 100644
--- a/gdb/serenity-nat.c
+++ b/gdb/serenity-nat.c
@@ -71,3 +71,17 @@ ptid_t serenity_nat_target::wait (ptid_t ptid, struct target_waitstatus* ourstat
return ptid_t (pid);
}
+
+void serenity_nat_target::mourn_inferior ()
+{
+ int status;
+
+ /* Wait just one more time to collect the inferior's exit status.
+ * Do not check whether this succeeds though, since we may be
+ * dealing with a process that we attached to. Such a process will
+ * only report its exit status to its original parent.
+ */
+ waitpid (inferior_ptid.pid (), &status, WNOHANG);
+
+ inf_child_target::mourn_inferior ();
+}
diff --git a/gdb/serenity-nat.h b/gdb/serenity-nat.h
index 9ae3b87..35d7ffc 100644
--- a/gdb/serenity-nat.h
+++ b/gdb/serenity-nat.h
@@ -13,6 +13,8 @@ class serenity_nat_target : public inf_ptrace_target
{
ptid_t wait (ptid_t, struct target_waitstatus *, target_wait_flags) override;
+ void mourn_inferior ();
+
private:
bool m_attach_before_continue_called { false };
};
--
2.32.0

26
Ports/gdb/patches/ReadMe.md
View file

@ -20,3 +20,29 @@ gdb: Add build support for SerenityOS
serenity: Fix compiler -fpermissive warnings from using latest GCC
## `0005-serenity-Implement-custom-wait-override-for-the-sere.patch`
serenity: Implement custom wait override for the serenity_nat_target
While troubleshooting why gdb wasn't working when attempting to debug
serenity programs I noticed two things:
- The contract of serenity's `waitpid(..)` appears to be slightly
different than the generic ptrace target expects. We need to make
sure we pass `WSTOPPED`, and it can return different errno values
that we would want to re-try on.
- The contract of serenity's `ptrace(..)` implementation appears to
diverge as well, as we are expected to call `PT_ATTACH` before we
call `PT_CONTINUE`, otherwise `ptrace(..)` will just error out.
Allow gdb to understand these differences, I've overloaded the
serenity_nat_target::wait(..) method and added the logic there.
## `0006-serenity-Implement-mourn_inferior-override-for-the-s.patch`
serenity: Implement mourn_inferior override for the serenity_nat_target
We need to pass `WNOHANG` to our `waitpid(..)` call on SerenityOS,
otherwise we will wait forever.