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| -rw-r--r-- | changelogs/changelog.md | 31 | ||||
| -rw-r--r-- | lib/std/sysrand.nim | 7 |
2 files changed, 37 insertions, 1 deletions
diff --git a/changelogs/changelog.md b/changelogs/changelog.md new file mode 100644 index 000000000..475f568ec --- /dev/null +++ b/changelogs/changelog.md @@ -0,0 +1,31 @@ +# v1.xx.x - yyyy-mm-dd + +## Changes affecting backward compatibility + +## Standard library additions and changes + +### New compile flag (`-d:nimNoGetRandom`) when building `std/sysrand` to remove dependency on linux `getrandom` syscall + +This compile flag only affects linux builds and is necessary if either compiling on a linux kernel version < 3.17, or if code built will be executing on kernel < 3.17. + +On linux kernels < 3.17 (such as kernel 3.10 in RHEL7 and CentOS7), the `getrandom` syscall was not yet introduced. Without this, the `std/sysrand` module will not build properly, and if code is built on a kernel >= 3.17 without the flag, any usage of the `std/sysrand` module will fail to execute on a kernel < 3.17 (since it attempts to perform a syscall to `getrandom`, which isn't present in the current kernel). A compile flag has been added to force the `std/sysrand` module to use /dev/urandom (available since linux kernel 1.3.30), rather than the `getrandom` syscall. This allows for use of a cryptographically secure PRNG, regardless of kernel support for the `getrandom` syscall. + +When building for RHEL7/CentOS7 for example, the entire build process for nim from a source package would then be: +```sh +$ yum install devtoolset-8 # Install GCC version 8 vs the standard 4.8.5 on RHEL7/CentOS7. Alternatively use -d:nimEmulateOverflowChecks. See issue #13692 for details +$ scl enable devtoolset-8 bash # Run bash shell with default toolchain of gcc 8 +$ sh build.sh # per unix install instructions +$ bin/nim c koch # per unix install instructions +$ ./koch boot -d:release # per unix install instructions +$ ./koch tools -d:nimNoGetRandom # pass the nimNoGetRandom flag to compile std/sysrand without support for getrandom syscall +``` + +This is necessary to pass when building nim on kernel versions < 3.17 in particular to avoid an error of "SYS_getrandom undeclared" during the build process for stdlib (sysrand in particular). + +## Language changes + + +## Compiler changes + + +## Tool changes diff --git a/lib/std/sysrand.nim b/lib/std/sysrand.nim index 75983e3c6..b35f24a72 100644 --- a/lib/std/sysrand.nim +++ b/lib/std/sysrand.nim @@ -38,6 +38,11 @@ ## .. _randomFillSync: https://nodejs.org/api/crypto.html#crypto_crypto_randomfillsync_buffer_offset_size ## .. _/dev/urandom: https://en.wikipedia.org/wiki//dev/random ## +## On a Linux target, a call to the `getrandom` syscall can be avoided (e.g. +## for targets running kernel version < 3.17) by passing a compile flag of +## `-d:nimNoGetRandom`. If this flag is passed, sysrand will use `/dev/urandom` +## as with any other POSIX compliant OS. +## runnableExamples: doAssert urandom(0).len == 0 @@ -159,7 +164,7 @@ elif defined(windows): result = randomBytes(addr dest[0], size) -elif defined(linux): +elif defined(linux) and not defined(nimNoGetRandom): # TODO using let, pending bootstrap >= 1.4.0 var SYS_getrandom {.importc: "SYS_getrandom", header: "<sys/syscall.h>".}: clong const syscallHeader = """#include <unistd.h> |