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getrandom() backwards compatibility shim #21158

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0xEAB wants to merge 3 commits into from
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getrandom() backwards compatibility shim #21158

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ffe33e8
Implement `version (linux_legacy_emulate_getrandom)`
0xEAB Apr 6, 2025
18e2340
Add changelog entry
0xEAB Apr 6, 2025
5cf44a3
Fix typo
0xEAB Apr 6, 2025
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19 changes: 19 additions & 0 deletions changelog/dmd.emulate_getrandom.dd
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
`getrandom()` backwards compatibility shim

To restore compatibility with older Linux platforms where `getrandom()` is
unavailable either due to an outdated kernel or a legacy C library, Phobos now
ships with a shim that emulates a limited subset of `getrandom()` by reading
random bytes from `/dev/urandom`.

To enable the shim, build DMD and Phobos with the environment variable
`LINUX_LEGACY_EMULATE_GETRANDOM` set to `1`.

```
cd phobos
LINUX_LEGACY_EMULATE_GETRANDOM=1 make
```

While this is actually Phobos feature, proper enablement requires compiler
support. This has been implemented by appending the version flag to the default
compiler configuration found in `dmd.conf`. Hence the DMD build script has been
made aware of this new option as well.
9 changes: 7 additions & 2 deletions compiler/src/build.d
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Expand Up @@ -305,19 +305,24 @@ DFLAGS=%DFLAGS% -L/OPT:NOICF
{
enum confFile = "dmd.conf";
enum conf = `[Environment32]
DFLAGS=-I%@P%/../../../../druntime/import -I%@P%/../../../../../phobos -L-L%@P%/../../../../../phobos/generated/{OS}/{BUILD}/32{exportDynamic} -fPIC
DFLAGS=-I%@P%/../../../../druntime/import -I%@P%/../../../../../phobos -L-L%@P%/../../../../../phobos/generated/{OS}/{BUILD}/32{exportDynamic}{extraVersions} -fPIC

[Environment64]
DFLAGS=-I%@P%/../../../../druntime/import -I%@P%/../../../../../phobos -L-L%@P%/../../../../../phobos/generated/{OS}/{BUILD}/64{exportDynamic} -fPIC
DFLAGS=-I%@P%/../../../../druntime/import -I%@P%/../../../../../phobos -L-L%@P%/../../../../../phobos/generated/{OS}/{BUILD}/64{exportDynamic}{extraVersions} -fPIC
`;
}

const extraVersions = (env.getNumberedBool("LINUX_LEGACY_EMULATE_GETRANDOM"))
? " -version=linux_legacy_emulate_getrandom"
: "";

builder
.name("dmdconf")
.target(env["G"].buildPath(confFile))
.msg("(TX) DMD_CONF")
.commandFunction(() {
const expConf = conf
.replace("{extraVersions}", extraVersions)
.replace("{exportDynamic}", exportDynamic)
.replace("{BUILD}", env["BUILD"])
.replace("{OS}", env["OS"]);
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