diff mbox series

[v2,19/38] gdbserver: enable POWER9 support

Message ID 20220329154931.493851-20-npiggin@gmail.com
State New
Headers show
Series gdbserver multi-threaded debugging and POWER9/10 support | expand

Commit Message

Nicholas Piggin March 29, 2022, 3:49 p.m. UTC 
POWER9 has a strange problem with attn, but otherwise gdbserver
works well. Enable it.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 README.md       | 14 +++++++++++---
 src/pdbgproxy.c | 29 +++++++++++++++++++++++++----
 2 files changed, 36 insertions(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/README.md b/README.md
index be26dc1..5c5c05d 100644
--- a/README.md
+++ b/README.md
@@ -527,8 +527,9 @@  There are also low level htm commands which can also be used:
  - `dump` will dump the trace to a file.
 
 ### GDBSERVER
-At the moment gdbserver is only supported on P8 while the cores are in the
-kernel. 
+At the moment gdbserver is only supported on P8 and P9.
+
+Memory access can only be performed on kernel memory.
 
 To run a gdbserver on a P8 machine from a BMC running openbmc:
 
@@ -540,7 +541,7 @@  $ ./pdbg -d p8 -p0 -c11 -t0 gdbserver 44
 
 On your local machine:
 $ gdb
-(gdb)  set architecture powerpc:common64
+(gdb) set architecture powerpc:common64
 (gdb) target remote palm5-bmc:44
 
 Debugging info:
@@ -559,6 +560,13 @@  Notes:
 happen.
 2. If you want to view the kernel call trace then run gdb on the vmlinux that
 the host is running (the kernel needs to be compiled with debug symbols).
+3. The kernel HARDLOCKUP watchdog can interact badly with GDBSERVER (and all
+pdbg direct controls for that matter). Disabling it before debugging is a
+good idea.
+4. Idle states have often had problems with pdbg direct controls. If things are
+misbehaving, booting Linux with powersave=off is the first thing to try.
+5. attn instructions seem to cause host hangs on POWER9. gdb breakpoints should
+not be used.
 
 ## Submitting patches
 
diff --git a/src/pdbgproxy.c b/src/pdbgproxy.c
index c7cab28..b3bf5bd 100644
--- a/src/pdbgproxy.c
+++ b/src/pdbgproxy.c
@@ -105,6 +105,9 @@  static void detach(uint64_t *stack, void *priv)
 
 #define POWER8_HID_ENABLE_ATTN			PPC_BIT(31)
 
+#define POWER9_HID_ENABLE_ATTN			PPC_BIT(3)
+#define POWER9_HID_FLUSH_ICACHE			PPC_BIT(2)
+
 static int set_attn(bool enable)
 {
 	uint64_t hid;
@@ -122,6 +125,17 @@  static int set_attn(bool enable)
 				return 0;
 			hid &= ~POWER8_HID_ENABLE_ATTN;
 		}
+	} else if (pdbg_target_compatible(thread_target, "ibm,power9-thread")) {
+		if (enable) {
+			if (hid & POWER9_HID_ENABLE_ATTN)
+				return 0;
+			hid |= POWER9_HID_ENABLE_ATTN;
+		} else {
+			if (!(hid & POWER9_HID_ENABLE_ATTN))
+				return 0;
+			hid &= ~POWER9_HID_ENABLE_ATTN;
+		}
+		hid |= POWER9_HID_FLUSH_ICACHE;
 	} else {
 		return -1;
 	}
@@ -658,13 +672,20 @@  static int gdbserver(uint16_t port)
 		return 0;
 	}
 
-	//
-	// Temporary until I can get this working a bit smoother on p9
-	if (!pdbg_target_compatible(thread, "ibm,power8-thread")) {
-		PR_ERROR("GDBSERVER is only available on POWER8\n");
+	if (!pdbg_target_compatible(thread, "ibm,power8-thread") &&
+	    !pdbg_target_compatible(thread, "ibm,power9-thread")) {
+		PR_ERROR("GDBSERVER is only available on POWER8 and POWER9\n");
 		return -1;
 	}
 
+	if (pdbg_target_compatible(thread, "ibm,power9-thread")) {
+		/*
+		 * XXX: If we advertise no swbreak support on POWER9 does
+		 * that prevent the client using them?
+		 */
+		PR_WARNING("Breakpoints may cause host crashes on POWER9 and should not be used\n");
+	}
+
 	/* Check endianess in MSR */
 	rc = thread_getmsr(thread, &msr);
 	if (rc) {