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Fix: Variadic function cast causing segfaults on Apple ARM64 #2708

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Merged
bjorng merged 1 commit into from
Aug 13, 2020
Merged

Fix: Variadic function cast causing segfaults on Apple ARM64 #2708

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18 changes: 9 additions & 9 deletions erts/emulator/beam/erl_db_util.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2031,7 +2031,7 @@ Eterm db_prog_match(Process *c_p,
Process *tmpp;
Process *current_scheduled;
ErtsSchedulerData *esdp;
Eterm (*bif)(Process*, ...);
BIF_RETTYPE (*bif)(BIF_ALIST);
Eterm bif_args[3];
int fail_label;
#ifdef DMC_DEBUG
Expand Down Expand Up @@ -2338,8 +2338,8 @@ Eterm db_prog_match(Process *c_p,
*esp++ = t;
break;
case matchCall0:
bif = (Eterm (*)(Process*, ...)) *pc++;
t = (*bif)(build_proc, bif_args);
bif = (BIF_RETTYPE (*)(BIF_ALIST)) *pc++;
t = (*bif)(build_proc, bif_args, NULL);
if (is_non_value(t)) {
if (do_catch)
t = FAIL_TERM;
Expand All @@ -2349,8 +2349,8 @@ Eterm db_prog_match(Process *c_p,
*esp++ = t;
break;
case matchCall1:
bif = (Eterm (*)(Process*, ...)) *pc++;
t = (*bif)(build_proc, esp-1);
bif = (BIF_RETTYPE (*)(BIF_ALIST)) *pc++;
t = (*bif)(build_proc, esp-1, NULL);
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@tehprofessor tehprofessor Aug 10, 2020 •
edited
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I think I've got everything updated correctly. The one thing I'm not entirely sure of is if this should be copied into bif_args, if this is an optimization for this specific case, or something else? I'm new to c; so, if I'm understanding this correctly, esp-1 works here without copying into bif_args because esp-1 and bif_args[0] essentially point to the same value and both are pointers so semantically it's all good? Then by not copying into bif_args[0] we save an allocation/step?

And, please feel free to tell me to just google more 😄 !

Thank you both for your time reviewing this, and please let me know if there's anything else I can change, improve, or have missed 😅 here.

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@bjorng bjorng Aug 10, 2020

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The copying of the arguments to bif_args when there are 2 or 3 arguments is only necessary because the arguments would be in the wrong order if we would pass esp-2 or esp-3, respectively. When there is a single argument, there is no need to copy it because it can't be in the wrong order.

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@tehprofessor tehprofessor Aug 10, 2020

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Thank you @bjorng

if (is_non_value(t)) {
if (do_catch)
t = FAIL_TERM;
Expand All @@ -2360,10 +2360,10 @@ Eterm db_prog_match(Process *c_p,
esp[-1] = t;
break;
case matchCall2:
bif = (Eterm (*)(Process*, ...)) *pc++;
bif = (BIF_RETTYPE (*)(BIF_ALIST)) *pc++;
bif_args[0] = esp[-1];
bif_args[1] = esp[-2];
t = (*bif)(build_proc, bif_args);
t = (*bif)(build_proc, bif_args, NULL);
if (is_non_value(t)) {
if (do_catch)
t = FAIL_TERM;
Expand All @@ -2374,11 +2374,11 @@ Eterm db_prog_match(Process *c_p,
esp[-1] = t;
break;
case matchCall3:
bif = (Eterm (*)(Process*, ...)) *pc++;
bif = (BIF_RETTYPE (*)(BIF_ALIST)) *pc++;
bif_args[0] = esp[-1];
bif_args[1] = esp[-2];
bif_args[2] = esp[-3];
t = (*bif)(build_proc, bif_args);
t = (*bif)(build_proc, bif_args, NULL);
if (is_non_value(t)) {
if (do_catch)
t = FAIL_TERM;
Expand Down