Here is a proposal to add printing of description of command line flags.
These descriptions are present in sources but they are not passed to the Flag structure.

There is an existing flag "-Xprintflags" that prints all flags and the default values.
This proposal extands that feature.

Here is a sample output of the proposed flag (formatting may go wrong below because of word wrapping)

java -server -XprintFlagsWithComments
[Global flags]
ccstr AbortVMOnException = {notproduct} Call fatal if this exception is thrown. Example: java -XX:AbortVMOnExcepion=java.lang.NullPointerException Foo
ccstr AbortVMOnExceptionMessage = {notproduct} Call fatal if the exception pointed by AbortVMOnException has this messag.
uintx AdaptivePermSizeWeight = 20 {product} Weight for perm gen exponential resizing, between 0 and 100
uintx AdaptiveSizeDecrementScaleFactor = 4 {product} Adaptive size scale down factor for shrinking
uintx AdaptiveSizeMajorGCDecayTimeScale = 10 {product} Time scale over which major costs decay
uintx AdaptiveSizePausePolicy = 0 {product} Policy for changing generation size for pause goals
uintx AdaptiveSizePolicyCollectionCostMargin = 50 {product} If collection costs are within margin, reduce both by ful delta
uintx AdaptiveSizePolicyGCTimeLimitThreshold = 5 Number of consecutive collections before gc time limit fires
uintx AdaptiveSizePolicyInitializingSteps = 20 {product} Number of steps where heuristics is used before data is used
uintx AdaptiveSizePolicyOutputInterval = 0 {product} Collecton interval for printing information; zero => never
uintx AdaptiveSizePolicyReadyThreshold = 5 Number of collections before the adaptive sizing is started
uintx AdaptiveSizePolicyWeight = 10 {product} Weight given to exponential resizing, between 0 and 100
uintx AdaptiveSizeThroughPutPolicy = 0 {product} Policy for changeing generation size for throughput goals
uintx AdaptiveTimeWeight = 25 {product} Weight given to time in adaptive policy, between 0 and 100
 bool AdjustConcurrency = false {product} call thr_setconcurrency at thread create time to avoid LWP sarvation on MP systems (For Solaris Only)
 bool AggressiveOpts = false {product} Enable aggressive optimizations - see arguments.cpp
 intx AliasLevel = 3 {product} 0 for no aliasing, 1 for oop/field/static/array split, 2 forclass split, 3 for unique instances
 intx AlignEntryCode = 4 aligns entry code to specified value (in bytes)
 intx AllocatePrefetchDistance = -1 {product} Distance to prefetch ahead of allocation pointer
.......