[PATCH] format_proc_cpuinfo: add microcode registry lookup values

[Brian Inglis]

Re: CPU microcode reported wrong in /proc/cpuinfo
    https://sourceware.org/pipermail/cygwin/2020-May/245063.html
earlier Windows releases used different registry values to store microcode
revisions depending on the MSR name being used to get microcode revisions:
add these alternative registry values to the cpuinfo registry value lookup;
iterate thru the registry data until a valid microcode revision is found;
some revision values are in the high bits, so if the low bits are all clear,
shift the revision value down into the low bits
---
 winsup/cygwin/fhandler_proc.cc | 44 +++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/winsup/cygwin/fhandler_proc.cc b/winsup/cygwin/fhandler_proc.cc
index f1bc1c7405..f637dfd8e4 100644
--- a/winsup/cygwin/fhandler_proc.cc
+++ b/winsup/cygwin/fhandler_proc.cc
@@ -692,26 +692,52 @@ format_proc_cpuinfo (void *, char *&destbuf)
       union
         {
          LONG uc_len;          /* -max size of buffer before call */
-         char uc_microcode[16];
-        } uc;
+         char uc_microcode[16];        /* at least 8 bytes */
+        } uc[4];               /* microcode values changed historically */
 
-      RTL_QUERY_REGISTRY_TABLE tab[3] =
+      RTL_QUERY_REGISTRY_TABLE tab[6] =
         {
          { NULL, RTL_QUERY_REGISTRY_DIRECT | RTL_QUERY_REGISTRY_NOSTRING,
-           L"~Mhz", &cpu_mhz, REG_NONE, NULL, 0 },
+           L"~Mhz",                   &cpu_mhz, REG_NONE, NULL, 0 },
          { NULL, RTL_QUERY_REGISTRY_DIRECT | RTL_QUERY_REGISTRY_NOSTRING,
-           L"Update Revision", &uc, REG_NONE, NULL, 0 },
+           L"Update Revision",          &uc[0], REG_NONE, NULL, 0 },
+                                                       /* latest MSR */
+         { NULL, RTL_QUERY_REGISTRY_DIRECT | RTL_QUERY_REGISTRY_NOSTRING,
+           L"Update Signature",         &uc[1], REG_NONE, NULL, 0 },
+                                                       /* previous MSR */
+         { NULL, RTL_QUERY_REGISTRY_DIRECT | RTL_QUERY_REGISTRY_NOSTRING,
+           L"CurrentPatchLevel",        &uc[2], REG_NONE, NULL, 0 },
+                                                       /* earlier MSR */
+         { NULL, RTL_QUERY_REGISTRY_DIRECT | RTL_QUERY_REGISTRY_NOSTRING,
+           L"Platform Specific Field1", &uc[3], REG_NONE, NULL, 0 },
+                                                       /* alternative */
          { NULL, 0, NULL, NULL, 0, NULL, 0 }
         };
 
-      memset (&uc, 0, sizeof (uc.uc_microcode));
-      uc.uc_len = -16; /* -max size of microcode buffer */
+      for (size_t uci = 0; uci < sizeof (uc)/sizeof (*uc); ++uci)
+       {
+         memset (&uc[uci], 0, sizeof (uc[uci]));
+         uc[uci].uc_len = -(LONG)sizeof (uc[0].uc_microcode);
+                                                       /* neg buffer size */
+       }
+
       RtlQueryRegistryValues (RTL_REGISTRY_ABSOLUTE, cpu_key, tab,
                              NULL, NULL);
       cpu_mhz = ((cpu_mhz - 1) / 10 + 1) * 10; /* round up to multiple of 10 */
       DWORD bogomips = cpu_mhz * 2; /* bogomips is double cpu MHz since MMX */
-      long long microcode = 0; /* at least 8 bytes for AMD */
-      memcpy (&microcode, &uc, sizeof (microcode));
+
+      unsigned long long microcode = 0;        /* needs 8 bytes */
+      for (size_t uci = 0; uci < sizeof (uc)/sizeof (*uc) && !microcode; ++uci)
+       {
+         /* still neg buffer size => no data */
+         if (-(LONG)sizeof (uc[uci].uc_microcode) != uc[uci].uc_len)
+           {
+             memcpy (&microcode, uc[uci].uc_microcode, sizeof (microcode));
+
+             if (!(microcode & 0xFFFFFFFFLL))  /* some values in high bits */
+                 microcode <<= 32;             /* shift them down */
+           }
+       }
 
       bufptr += __small_sprintf (bufptr, "processor\t: %d\n", cpu_number);
       uint32_t maxf, vendor_id[4], unused;
-- 
2.27.0