From ccb8b3096711bc9b371af371d399da7f47e4fe50 Mon Sep 17 00:00:00 2001
From: Richard Cooper <richard.cooper@arm.com>
Date: Wed, 22 Nov 2023 08:59:01 +0000
Subject: [PATCH] misc: Update Dmesg dump for changes to printk in Linux
 v5.18+.

Linux v5.18+ changed the format of one of the data structures used to
implement the printk ring buffer. This caused the gem5 feature to dump
the printk messages on Kernel panic to fail for Kernels 5.18.0 and
later.

This patch updates the printk messages dump feature to support the new
printk ring buffer format when Kernels 5.18 and later are detected.

This patch addresses gem5 Issue #550:
https://github.com/gem5/gem5/issues/550

Change-Id: I533d539eafb83c44eeb4b9fbbcdd9c172fd398e6
Reported-by: Hoa Nguyen <hn@hnpl.org>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
---
 src/kern/linux/helpers.cc | 83 +++++++++++++++++++++++++++++++--------
 1 file changed, 67 insertions(+), 16 deletions(-)

diff --git a/src/kern/linux/helpers.cc b/src/kern/linux/helpers.cc
index d153a75504..97b363c864 100644
--- a/src/kern/linux/helpers.cc
+++ b/src/kern/linux/helpers.cc
@@ -266,6 +266,41 @@ struct GEM5_PACKED DmesgInfoRecord
     }
 };
 
+/** Metadata struct for Linux pre-v5.18.0
+ *
+ */
+template<typename AtomicVarType>
+struct Metadata_Pre_v5_18_0
+{
+    using atomic_var_t = AtomicVarType;
+    using guest_ptr_t =
+        typename std::make_unsigned_t<atomic_var_t>;
+    unsigned int mask_bits;
+    guest_ptr_t metadata_ring_ptr;
+    guest_ptr_t info_ring_ptr;
+    atomic_var_t unused1;
+    atomic_var_t unused2;
+};
+
+
+/** Metadata struct for Linux post-v5.18.0
+ *
+ */
+template<typename AtomicVarType>
+struct Metadata_Post_v5_18_0
+{
+    using atomic_var_t = AtomicVarType;
+    using guest_ptr_t =
+        typename std::make_unsigned_t<atomic_var_t>;
+    unsigned int mask_bits;
+    guest_ptr_t metadata_ring_ptr;
+    guest_ptr_t info_ring_ptr;
+    atomic_var_t unused1;
+    atomic_var_t unused2;
+    atomic_var_t unused3;
+};
+
+
 /** Top-level ringbuffer record for the Linux dmesg ringbuffer, post-v5.10.
  *
  *  Struct data members are compatible with the equivalent Linux data
@@ -276,7 +311,7 @@ struct GEM5_PACKED DmesgInfoRecord
  *  the gem5 world, and reading/generating appropriate masks.
  *
  */
-template<typename AtomicVarType>
+template<typename AtomicVarType, typename MetadataStructType>
 struct GEM5_PACKED DmesgRingbuffer
 {
     static_assert(
@@ -291,14 +326,9 @@ struct GEM5_PACKED DmesgRingbuffer
     using metadata_record_t = DmesgMetadataRecord<atomic_var_t>;
 
     // Struct data members
-    struct
-    {
-        unsigned int mask_bits;
-        guest_ptr_t metadata_ring_ptr;
-        guest_ptr_t info_ring_ptr;
-        atomic_var_t unused1;
-        atomic_var_t unused2;
-    } metadata;
+
+    // Metadata struct size depends on the Linux Kernel Version
+    MetadataStructType metadata;
     struct
     {
         unsigned int mask_bits;
@@ -391,9 +421,16 @@ struct GEM5_PACKED DmesgRingbuffer
     }
 };
 
-// Aliases for the two types of Ringbuffer that could be used.
-using Linux64_Ringbuffer = DmesgRingbuffer<int64_t>;
-using Linux32_Ringbuffer = DmesgRingbuffer<int32_t>;
+// Aliases for the types of Ringbuffer that could be used.
+using Linux64_Ringbuffer_Pre_v5_18_0 =
+    DmesgRingbuffer<int64_t, Metadata_Pre_v5_18_0<int64_t>>;
+using Linux32_Ringbuffer_Pre_v5_18_0 =
+    DmesgRingbuffer<int32_t, Metadata_Pre_v5_18_0<int32_t>>;
+
+using Linux64_Ringbuffer_Post_v5_18_0 =
+    DmesgRingbuffer<int64_t, Metadata_Post_v5_18_0<int64_t>>;
+using Linux32_Ringbuffer_Post_v5_18_0 =
+    DmesgRingbuffer<int32_t, Metadata_Post_v5_18_0<int32_t>>;
 
 /** Print the record at the specified offset into the data ringbuffer,
  *  and return the offset of the next entry in the data ringbuffer,
@@ -635,7 +672,6 @@ extract_printable_strings(const std::vector<uint8_t> buffer)
  * If no likely match is found, 0x0 is returned to indicate an error.
  *
  */
-[[maybe_unused]]
 uint32_t
 extract_kernel_version(ThreadContext* tc) {
     System *system = tc->getSystemPtr();
@@ -695,11 +731,26 @@ dumpDmesg(ThreadContext *tc, std::ostream &os)
 {
     System *system = tc->getSystemPtr();
     const bool os_is_64_bit = loader::archIs64Bit(system->workload->getArch());
+    const uint32_t kernel_version = extract_kernel_version(tc);
+    const uint32_t KERNEL_5_18_0 = 0x00051200;
 
-    if (os_is_64_bit) {
-        dumpDmesgImpl<Linux64_Ringbuffer>(tc, os);
+    if (kernel_version == 0x0) {
+        warn("Could not determine Linux Kernel version. "
+             "Assuming post-v5.18.0\n");
+    }
+
+    if (kernel_version == 0x0 || kernel_version >= KERNEL_5_18_0) {
+        if (os_is_64_bit) {
+            dumpDmesgImpl<Linux64_Ringbuffer_Post_v5_18_0>(tc, os);
+        } else {
+            dumpDmesgImpl<Linux32_Ringbuffer_Post_v5_18_0>(tc, os);
+        }
     } else {
-        dumpDmesgImpl<Linux32_Ringbuffer>(tc, os);
+        if (os_is_64_bit) {
+            dumpDmesgImpl<Linux64_Ringbuffer_Pre_v5_18_0>(tc, os);
+        } else {
+            dumpDmesgImpl<Linux32_Ringbuffer_Pre_v5_18_0>(tc, os);
+        }
     }
 }