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Re: [PATCH 4/5] gzip: move crc state into consilidated gzip state


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
  • Date: Fri, 12 Apr 2024 07:42:22 -0400
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  • Cc: Jason Andryuk <jason.andryuk@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • Delivery-date: Fri, 12 Apr 2024 11:42:31 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 4/11/24 15:43, Andrew Cooper wrote:
On 11/04/2024 4:25 pm, Daniel P. Smith wrote:
diff --git a/xen/common/gzip/inflate.c b/xen/common/gzip/inflate.c
index c8dd35962abb..6c8c7452a31f 100644
--- a/xen/common/gzip/inflate.c
+++ b/xen/common/gzip/inflate.c
@@ -1125,16 +1125,14 @@ static int __init inflate(struct gzip_data *gd)
   *
   **********************************************************************/
-static ulg __initdata crc_32_tab[256];
-static ulg __initdata crc;  /* initialized in makecrc() so it'll reside in bss 
*/
-#define CRC_VALUE (crc ^ 0xffffffffUL)
+#define CRC_VALUE (gd->crc ^ 0xffffffffUL)
/*
   * Code to compute the CRC-32 table. Borrowed from
   * gzip-1.0.3/makecrc.c.
   */
-static void __init makecrc(void)
+static void __init makecrc(struct gzip_data *gd)
  {
  /* Not copyrighted 1990 Mark Adler */
@@ -1151,7 +1149,7 @@ static void __init makecrc(void)
      for (i = 0; i < sizeof(p)/sizeof(int); i++)
          e |= 1L << (31 - p[i]);
- crc_32_tab[0] = 0;
+    gd->crc_32_tab[0] = 0;
for (i = 1; i < 256; i++)
      {
@@ -1162,11 +1160,11 @@ static void __init makecrc(void)
              if (k & 1)
                  c ^= e;
          }
-        crc_32_tab[i] = c;
+        gd->crc_32_tab[i] = c;
      }
/* this is initialized here so this code could reside in ROM */
-    crc = (ulg)0xffffffffUL; /* shift register contents */
+    gd->crc = (ulg)0xffffffffUL; /* shift register contents */
  }
/* gzip flag byte */

I can't see any way that a non-32bit value ever gets stored, because 'e'
doesn't ever have bit 32 set in it.  I have a sneaking suspicion that
this is code written in the 32bit days, where sizeof(long) was still 4.

Yes, I can switch crc and crc_32_tab to uint32_t.

This change, if correct, halves the size of gzip_state.

Ack.

v/r,
dps



 


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