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authorBjörn Gustavsson <[email protected]>2018-12-05 18:00:17 +0100
committerBjörn Gustavsson <[email protected]>2018-12-06 10:40:48 +0100
commitf19a52e92ae56b8e5248064db56dc38c0d7dff69 (patch)
treefe74484ec40a398eae8c0a1decc7567320225211 /erts/emulator/utils
parentc85094dddfa54bb3991d7ba6147ef177c0dd9c42 (diff)
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beam_makeops: Correct generation of pack instructions
On a 32-bit machine, `beam_makeops` would generate incorrect pack instructions for instructions such as: i_plus x x j? d See the added comment block for a detailed description of the problem and its fix.
Diffstat (limited to 'erts/emulator/utils')
-rwxr-xr-xerts/emulator/utils/beam_makeops57
1 files changed, 51 insertions, 6 deletions
diff --git a/erts/emulator/utils/beam_makeops b/erts/emulator/utils/beam_makeops
index da994fae3e..f73e2362bf 100755
--- a/erts/emulator/utils/beam_makeops
+++ b/erts/emulator/utils/beam_makeops
@@ -1840,12 +1840,57 @@ sub do_pack_one {
}
#
- # Return if there is nothing to pack.
- #
- if ($packable_args == 0) {
- return (-1);
- } elsif ($packable_args == 1 and $options == 0) {
- return (-1);
+ # Check whether any packing can be done.
+ #
+ my $nothing_to_pack = $packable_args == 0 ||
+ $packable_args == 1 && $options == 0;
+ if ($nothing_to_pack) {
+ # The packing engine in the loader processes the operands from
+ # right to left. Rightmost operands that are not packed must
+ # be stacked and then unstacked.
+ #
+ # Because instructions may be broken up into micro
+ # instructions, we might not see all operands at once. So
+ # there could be a micro instructions that packs the operands
+ # to the left of the current micro instruction. If that is the
+ # case, it is essential that we generate stacking and
+ # unstacking instructions even when no packing is
+ # possible. (build_pack_spec() will remove any unecessary
+ # stacking and unstacking operations.)
+ #
+ # Here is an example. Say that we have this instruction:
+ #
+ # i_plus x x j d
+ #
+ # that comprises two micro instructions:
+ #
+ # i_plus.fetch x x
+ # i_plus.execute j d
+ #
+ # This function (do_pack_one()) will be called twice, once to pack
+ # 'x' and 'x', and once to pack 'j' and 'd'.
+ #
+ # On a 32-bit machine, the 'j' and 'd' operands can't be
+ # packed because 'j' requires a full word. The two 'x'
+ # operands in the i_plus.fetch micro instruction will be
+ # packed, though, so we must generate instructions for packing
+ # and unpacking the 'j' and 'd' operands.
+ my $down = '';
+ my $up = '';
+ foreach my $arg (@args) {
+ my $push = 'g';
+ if ($type_bit{$arg} & $type_bit{'q'}) {
+ # The operand may be a literal.
+ $push = 'q';
+ } elsif ($type_bit{$arg} & $type_bit{'f'}) {
+ # The operand may be a failure label.
+ $push = 'f';
+ }
+ $down = "$push${down}";
+ $up = "${up}p";
+ }
+ my $pack_spec = "$down:$up";
+ return (1, ['',$pack_spec,@args]);
}
#