bugTiny C Compiler - Bugs: bug #51169, tcc miscompiles unsigned long long...


bug #51169: tcc miscompiles unsigned long long bitfields

Submitter:  Tony Garnock-Jones <surazal>
Submitted:  Sat 03 Jun 2017 03:04:50 PM UTC
Category:  None Severity:  3 - Normal
Item Group:  None Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open
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Sat 03 Jun 2017 05:00:50 PM UTC, comment #1: 

Could the following patch be a step toward a fix? (Also attached)

diff --git a/tccgen.c b/tccgen.c
index 1a8ba3d..68fcd19 100644
--- a/tccgen.c
+++ b/tccgen.c
@@ -5750,11 +5750,13 @@ static void block(int *bsym, int *csym, int is_expr)
         for (b = 1; b < sw.n; b++)
             if (sw.p[b - 1]->v2 >= sw.p[b]->v1)
                 tcc_error("duplicate case value");
+        vpushv(&switchval);
         /* Our switch table sorting is signed, so the compared
            value needs to be as well when it's 64bit.  */
-        if ((switchval.type.t & VT_BTYPE) == VT_LLONG)
-            switchval.type.t &= ~VT_UNSIGNED;
-        vpushv(&switchval);
+        if ((switchval.type.t & VT_BTYPE) == VT_LLONG) {
+            switchval.type.t = VT_LLONG;
+            gen_cast(&switchval.type);
+        }
         gcase(sw.p, sw.n, &a);
         if (sw.def_sym)

Tony Garnock-Jones <surazal>
Sat 03 Jun 2017 03:04:50 PM UTC, original submission:  

This is using tcc:i386 on Debian,
tcc version 0.9.27 (prerelease) (i386 Linux)

The following program should produce exit status 0, but produces exit status 1.

The problem is that it is using SAR instead of SHR to extract the bit field in the switch.

struct foo {
  unsigned long long t: 4;
  unsigned long long s: 60;

void init_foo(struct foo *f) {
  f->t = 8;
  f->s = 0;

int main(int argc, char *argv[]) {
  struct foo f;
  switch (f.t) {
    case 8:
      return 0;
      return 1;

Tony Garnock-Jones <surazal>


(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:

Attached Files
file #40848:  t.c added by surazal (277B - text/x-csrc)


Depends on the following items: None found

Items that depend on this one: None found


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  • -email is unavailable- added by surazal (Submitted the item)

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    Follow 2 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2017-06-03 surazal Attached File- Added experimental-bug51169.patch, #40849
    2017-06-03 surazal Attached File- Added t.c, #40848

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